Print non-Ada unions without crashing

ada-lang.c is a bit too eager trying to decode unions in the Ada style
-- looking for discriminants and such.  This causes crashes when
printing a non-Ada union in Ada mode, something that can easily happen
when printing a value from history or certain registers on AArch64.

This patch fixes the bug by changing ada-lang.c to only apply special
Ada treatment to types coming from an Ada CU.  This in turn required a
couple of surprising changes.

First, some of the Ada code was already using HAVE_GNAT_AUX_INFO to
decide whether a type had already been fixed -- such types had
INIT_CPLUS_SPECIFIC called on them.  This patch changes these spots to
use the "none" identifier instead.

This then required changing value_rtti_type to avoid changing the
language-specific object attached to an Ada type, which seems like a
good change regardless.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-04-19  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_is_variant_part, ada_to_fixed_type_1):
	Check ADA_TYPE_P.
	(empty_record, ada_template_to_fixed_record_type_1)
	(template_to_static_fixed_type)
	(to_record_with_fixed_variant_part): Use INIT_NONE_SPECIFIC.
	* cp-abi.c (value_rtti_type): Check HAVE_CPLUS_STRUCT.
	* gdbtypes.h (INIT_NONE_SPECIFIC, ADA_TYPE_P): New
	macros.

gdb/testsuite/ChangeLog
2019-04-19  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/ptype_union.c: New file.
	* gdb.ada/ptype_union.exp: New file.

3 files changed, 80 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 89058f4..aaa110c 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2019-04-19  Tom Tromey  <tromey@adacore.com>
 
+	* gdb.ada/ptype_union.c: New file.
+	* gdb.ada/ptype_union.exp: New file.
+
+2019-04-19  Tom Tromey  <tromey@adacore.com>
+
 	PR symtab/24423:
 	* gdb.base/list0.h (foo): Add a control-l character.
 
diff --git a/gdb/testsuite/gdb.ada/ptype_union.c b/gdb/testsuite/gdb.ada/ptype_union.c
new file mode 100644
index 0000000..eef9c5a
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/ptype_union.c
@@ -0,0 +1,41 @@
+/* This test program is part of GDB, the GNU debugger.
+
+   Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+union a
+{
+  int l;
+  double m;
+};
+
+union b
+{
+  char *n;
+  float o;
+};
+
+struct s
+{
+  union a af;
+  union b bf;
+};
+
+struct s global;
+
+int main ()
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.ada/ptype_union.exp b/gdb/testsuite/gdb.ada/ptype_union.exp
new file mode 100644
index 0000000..4f33721
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/ptype_union.exp
@@ -0,0 +1,34 @@
+# Copyright 2019 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile .c
+
+if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
+    return -1
+}
+
+# The test case is written in C, because it was easy to make the
+# required type there; but the bug itself only happens in Ada.
+gdb_test "set lang ada" ""
+
+gdb_test "ptype global" \
+    [multi_line \
+	 "type = record" \
+	 "\[ \t\]*af: a;" \
+	 "\[ \t\]*bf: b;" \
+	 "end record"]
+
+gdb_test "print global" \
+    " = \\(af => \\(l => 0, m => 0.0\\), bf => \\(n => 0x0, o => 0.0\\)\\)"