ada: Rework s-linux/osinte for arm/aarch64-android sigactions

Building an aarch64-android compiler with the current sources
initially intended for arm-android expectedly trips on problems.

This change is meant to address:
```
.../gcc/ada/rts % ../../gnat1 -quiet ... a-stbufi.adb -I.

s-osinte.ads:591:07: error: component "sa_flags" overlaps "sa_mask" at line 590
```

s-linux__android.ads makes hardcoded assumptions on the size
of sigset_t, based on observations performed in the course of the
arm port.

Then sysem headers show sa_flags placed VERY differently between
the 32 and the 64 bits variants.

See android-sysroot/usr/include/bits/signal_types.h
```
%if defined(__LP64__)

  int sa_flags; \
  union { \
    sighandler_t sa_handler; \
    void (*sa_sigaction)(int, struct siginfo*, void*); \
  }; \
  sigset_t sa_mask; \
  void (*sa_restorer)(void); \

%else

  union {
    sighandler_t sa_handler;
    void (*sa_sigaction)(int, struct siginfo*, void*);
  };
  sigset_t sa_mask;
  int sa_flags;
  void (*sa_restorer)(void);

```

gcc/ada/ChangeLog:

	* libgnarl/s-linux__android-arm.ads: New file, renaming of ...
	* libgnarl/s-linux__android.ads: ... this file.
	* libgnarl/s-linux__android-aarch64.ads: New file. Based on the
	-arm variant, with sa_ field positions adjusted.
	* Makefile.rtl (arm/aarch64-android pairs): Adjust accordingly.
	* libgnarl/s-osinte__android.ads: Rather than making assumptions
	on the actual type of the C sigset_t, use
	Os_Constants.SIZEOF_sigset_t to define an Ada sigset_t type of the
	proper size. Use C.int instead of unsigned_long for sa_flags.

4 files changed, 143 insertions, 5 deletions

diff --git a/gcc/ada/Makefile.rtl b/gcc/ada/Makefile.rtl
index 9f4c6cd..d4607e9 100644
--- a/gcc/ada/Makefile.rtl
+++ b/gcc/ada/Makefile.rtl
@@ -1414,7 +1414,6 @@ ifeq ($(strip $(filter-out arm% aarch64 linux-android%,$(target_cpu) $(target_os
   a-intnam.ads<libgnarl/a-intnam__linux.ads \
   s-inmaop.adb<libgnarl/s-inmaop__posix.adb \
   s-intman.adb<libgnarl/s-intman__android.adb \
-  s-linux.ads<libgnarl/s-linux__android.ads \
   s-osinte.adb<libgnarl/s-osinte__android.adb \
   s-osinte.ads<libgnarl/s-osinte__android.ads \
   s-oslock.ads<libgnat/s-oslock__posix.ads \
@@ -1439,11 +1438,15 @@ ifeq ($(strip $(filter-out arm% aarch64 linux-android%,$(target_cpu) $(target_os
 
      EH_MECHANISM=-arm
      SIGTRAMP_OBJ=sigtramp-armdroid.o
+     LIBGNAT_TARGET_PAIRS += \
+       s-linux.ads<libgnarl/s-linux__android-arm.ads
   else
      SELECTED_PAIRS=aarch64-android
 
      EH_MECHANISM=-gcc
      SIGTRAMP_OBJ=
+     LIBGNAT_TARGET_PAIRS += \
+       s-linux.ads<libgnarl/s-linux__android-aarch64.ads
 
      LIBGNAT_TARGET_PAIRS += $(GNATRTL_128BIT_PAIRS)
      EXTRA_GNATRTL_NONTASKING_OBJS = $(GNATRTL_128BIT_OBJS)
diff --git a/gcc/ada/libgnarl/s-linux__android-aarch64.ads b/gcc/ada/libgnarl/s-linux__android-aarch64.ads
new file mode 100644
index 0000000..6c64626
--- /dev/null
+++ b/gcc/ada/libgnarl/s-linux__android-aarch64.ads
@@ -0,0 +1,133 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
+--                                                                          --
+--                          S Y S T E M .  L I N U X                        --
+--                                                                          --
+--                                  S p e c                                 --
+--                                                                          --
+--            Copyright (C) 2014-2024, Free Software Foundation, Inc.       --
+--                                                                          --
+-- GNARL is free software; you can  redistribute it  and/or modify it under --
+-- terms of the  GNU General Public License as published  by the Free Soft- --
+-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
+-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
+-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
+-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
+--                                                                          --
+-- As a special exception under Section 7 of GPL version 3, you are granted --
+-- additional permissions described in the GCC Runtime Library Exception,   --
+-- version 3.1, as published by the Free Software Foundation.               --
+--                                                                          --
+-- In particular,  you can freely  distribute your programs  built with the --
+-- GNAT Pro compiler, including any required library run-time units,  using --
+-- any licensing terms  of your choosing.  See the AdaCore Software License --
+-- for full details.                                                        --
+--                                                                          --
+--                                                                          --
+------------------------------------------------------------------------------
+
+--  This is the Android version of this package
+
+--  This package encapsulates cpu specific differences between implementations
+--  of GNU/Linux, in order to share s-osinte-linux.ads.
+
+--  PLEASE DO NOT add any with-clauses to this package or remove the pragma
+--  Preelaborate. This package is designed to be a bottom-level (leaf) package
+
+with Interfaces.C;
+with System.Parameters;
+
+package System.Linux is
+   pragma Preelaborate;
+
+   ----------
+   -- Time --
+   ----------
+
+   subtype long        is Interfaces.C.long;
+   subtype suseconds_t is Interfaces.C.long;
+   type time_t is range -2 ** (System.Parameters.time_t_bits - 1)
+     .. 2 ** (System.Parameters.time_t_bits - 1) - 1;
+   subtype clockid_t   is Interfaces.C.int;
+
+   type timespec is record
+      tv_sec  : time_t;
+      tv_nsec : long;
+   end record;
+   pragma Convention (C, timespec);
+
+   type timeval is record
+      tv_sec  : time_t;
+      tv_usec : suseconds_t;
+   end record;
+   pragma Convention (C, timeval);
+
+   -----------
+   -- Errno --
+   -----------
+
+   EAGAIN    : constant := 11;
+   EINTR     : constant := 4;
+   EINVAL    : constant := 22;
+   ENOMEM    : constant := 12;
+   EPERM     : constant := 1;
+   ETIMEDOUT : constant := 110;
+
+   -------------
+   -- Signals --
+   -------------
+
+   SIGHUP     : constant := 1; --  hangup
+   SIGINT     : constant := 2; --  interrupt (rubout)
+   SIGQUIT    : constant := 3; --  quit (ASCD FS)
+   SIGILL     : constant := 4; --  illegal instruction (not reset)
+   SIGTRAP    : constant := 5; --  trace trap (not reset)
+   SIGIOT     : constant := 6; --  IOT instruction
+   SIGABRT    : constant := 6; --  used by abort, replace SIGIOT in the future
+   SIGFPE     : constant := 8; --  floating point exception
+   SIGKILL    : constant := 9; --  kill (cannot be caught or ignored)
+   SIGBUS     : constant := 7; --  bus error
+   SIGSEGV    : constant := 11; --  segmentation violation
+   SIGPIPE    : constant := 13; --  write on a pipe with no one to read it
+   SIGALRM    : constant := 14; --  alarm clock
+   SIGTERM    : constant := 15; --  software termination signal from kill
+   SIGUSR1    : constant := 10; --  user defined signal 1
+   SIGUSR2    : constant := 12; --  user defined signal 2
+   SIGCLD     : constant := 17; --  alias for SIGCHLD
+   SIGCHLD    : constant := 17; --  child status change
+   SIGPWR     : constant := 30; --  power-fail restart
+   SIGWINCH   : constant := 28; --  window size change
+   SIGURG     : constant := 23; --  urgent condition on IO channel
+   SIGPOLL    : constant := 29; --  pollable event occurred
+   SIGIO      : constant := 29; --  I/O now possible (4.2 BSD)
+   SIGLOST    : constant := 29; --  File lock lost
+   SIGSTOP    : constant := 19; --  stop (cannot be caught or ignored)
+   SIGTSTP    : constant := 20; --  user stop requested from tty
+   SIGCONT    : constant := 18; --  stopped process has been continued
+   SIGTTIN    : constant := 21; --  background tty read attempted
+   SIGTTOU    : constant := 22; --  background tty write attempted
+   SIGVTALRM  : constant := 26; --  virtual timer expired
+   SIGPROF    : constant := 27; --  profiling timer expired
+   SIGXCPU    : constant := 24; --  CPU time limit exceeded
+   SIGXFSZ    : constant := 25; --  filesize limit exceeded
+   SIGUNUSED  : constant := 31; --  unused signal (GNU/Linux)
+   SIGSTKFLT  : constant := 16; --  coprocessor stack fault (Linux)
+   SIG32      : constant := 32; --  glibc internal signal
+   SIG33      : constant := 33; --  glibc internal signal
+   SIG34      : constant := 34; --  glibc internal signal
+
+   --  struct_sigaction offsets
+
+   --  sa_flags come first on aarch64-android (sa_flags, sa_handler, sa_mask)
+
+   sa_flags_pos   : constant := 0;
+   sa_handler_pos : constant := sa_flags_pos + Interfaces.C.int'Size / 8;
+   sa_mask_pos    : constant := sa_handler_pos + Standard'Address_Size / 8;
+
+   SA_SIGINFO  : constant := 16#00000004#;
+   SA_ONSTACK  : constant := 16#08000000#;
+   SA_RESTART  : constant := 16#10000000#;
+   SA_NODEFER  : constant := 16#40000000#;
+
+end System.Linux;
diff --git a/gcc/ada/libgnarl/s-linux__android.ads b/gcc/ada/libgnarl/s-linux__android-arm.ads
index ff369d5..ff369d5 100644
--- a/gcc/ada/libgnarl/s-linux__android.ads
+++ b/gcc/ada/libgnarl/s-linux__android-arm.ads
diff --git a/gcc/ada/libgnarl/s-osinte__android.ads b/gcc/ada/libgnarl/s-osinte__android.ads
index 8e1b5a2..6238906 100644
--- a/gcc/ada/libgnarl/s-osinte__android.ads
+++ b/gcc/ada/libgnarl/s-osinte__android.ads
@@ -175,7 +175,7 @@ package System.OS_Interface is
    type struct_sigaction is record
       sa_handler  : System.Address;
       sa_mask     : sigset_t;
-      sa_flags    : Interfaces.C.unsigned_long;
+      sa_flags    : Interfaces.C.int;
       sa_restorer : System.Address;
    end record;
    pragma Convention (C, struct_sigaction);
@@ -580,16 +580,18 @@ package System.OS_Interface is
 
 private
 
-   type sigset_t is new Interfaces.C.unsigned_long;
+   type sigset_t is
+     array (0 .. OS_Constants.SIZEOF_sigset - 1) of unsigned_char;
    pragma Convention (C, sigset_t);
    for sigset_t'Alignment use Interfaces.C.unsigned_long'Alignment;
 
    pragma Warnings (Off);
    for struct_sigaction use record
       sa_handler at Linux.sa_handler_pos range 0 .. Standard'Address_Size - 1;
-      sa_mask    at Linux.sa_mask_pos range 0 .. sigset_t'Size - 1;
+      sa_mask    at Linux.sa_mask_pos
+        range 0 .. OS_Constants.SIZEOF_sigset * 8 - 1;
       sa_flags   at Linux.sa_flags_pos
-        range 0 .. Interfaces.C.unsigned_long'Size - 1;
+        range 0 .. Interfaces.C.int'Size - 1;
    end record;
    --  We intentionally leave sa_restorer unspecified and let the compiler
    --  append it after the last field, so disable corresponding warning.