gdb: fix gdbarch_tdep ODR violation

I would like to be able to use non-trivial types in gdbarch_tdep types.
This is not possible at the moment (in theory), because of the one
definition rule.

To allow it, rename all gdbarch_tdep types to <arch>_gdbarch_tdep, and
make them inherit from a gdbarch_tdep base class.  The inheritance is
necessary to be able to pass pointers to all these <arch>_gdbarch_tdep
objects to gdbarch_alloc, which takes a pointer to gdbarch_tdep.

These objects are never deleted through a base class pointer, so I
didn't include a virtual destructor.  In the future, if gdbarch objects
deletable, I could imagine that the gdbarch_tdep objects could become
owned by the gdbarch objects, and then it would become useful to have a
virtual destructor (so that the gdbarch object can delete the owned
gdbarch_tdep object).  But that's not necessary right now.

It turns out that RISC-V already has a gdbarch_tdep that is
non-default-constructible, so that provides a good motivation for this
change.

Most changes are fairly straightforward, mostly needing to add some
casts all over the place.  There is however the xtensa architecture,
doing its own little weird thing to define its gdbarch_tdep.  I did my
best to adapt it, but I can't test those changes.

Change-Id: Ic001903f91ddd106bd6ca09a79dabe8df2d69f3b

1 files changed, 7 insertions, 7 deletions

diff --git a/gdb/arc-tdep.h b/gdb/arc-tdep.h
index 8bb005c..d8495ed 100644
--- a/gdb/arc-tdep.h
+++ b/gdb/arc-tdep.h
@@ -121,27 +121,27 @@ extern bool arc_debug;
 
 /* Target-dependent information.  */
 
-struct gdbarch_tdep
+struct arc_gdbarch_tdep : gdbarch_tdep
 {
   /* Offset to PC value in jump buffer.  If this is negative, longjmp
      support will be disabled.  */
-  int jb_pc;
+  int jb_pc = 0;
 
   /* Whether target has hardware (aka zero-delay) loops.  */
-  bool has_hw_loops;
+  bool has_hw_loops = false;
 
   /* Detect sigtramp.  */
-  bool (*is_sigtramp) (struct frame_info *);
+  bool (*is_sigtramp) (struct frame_info *) = nullptr;
 
   /* Get address of sigcontext for sigtramp.  */
-  CORE_ADDR (*sigcontext_addr) (struct frame_info *);
+  CORE_ADDR (*sigcontext_addr) (struct frame_info *) = nullptr;
 
   /* Offset of registers in `struct sigcontext'.  */
-  const int *sc_reg_offset;
+  const int *sc_reg_offset = nullptr;
 
   /* Number of registers in sc_reg_offsets.  Most likely a ARC_LAST_REGNUM,
      but in theory it could be less, so it is kept separate.  */
-  int sc_num_regs;
+  int sc_num_regs = 0;
 };
 
 /* Utility functions used by other ARC-specific modules.  */