compile: Warn for old GCC on cv-qualified self-reference

GDB could:

compile code struct_object.selffield = &struct_object
./compile/compile-c-types.c:83: internal-error: insert_type: Assertion `add == NULL || add->gcc_type == gcc_type' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n) FAIL: gdb.compile/compile.exp: compile code struct_object.selffield = &struct_object (GDB internal
error)

The bug was not in GDB but in the GCC part interfacing with GDB.

Alexandre Oliva has fixed it the right way:
	https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;a=commitdiff;h=072dfdba0ea62abb65514cb3a90cdf3868efe286
	git://gcc.gnu.org/git/gcc.git
	aoliva/libcp1

Attaching this GDB testsuite update + info to user s/he should upgrade GCC.
After Alex upstreams the fix I can update the message to contain the specific
GCC release.

gdb/ChangeLog
2015-07-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	PR compile/18484
	* compile/compile-c-types.c (insert_type): Change gdb_assert to error.

gdb/testsuite/ChangeLog
2015-07-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	PR compile/18484
	* gdb.compile/compile.c (struct struct_type): Add volatile to
	selffield's type.
	* gdb.compile/compile.exp
	(compile code struct_object.selffield = &struct_object): Skip further
	struct_object tests if this one xfails.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2015-07-08  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	PR compile/18484
+	* compile/compile-c-types.c (insert_type): Change gdb_assert to error.
+
 2015-07-08  Robert O'Callahan  <robert@ocallahan.org>
 
 	PR exp/18617

gdb/compile/compile-c-types.c

@@ -78,7 +78,8 @@ insert_type (struct compile_c_instance *context, struct type *type,
   add = *slot;
   /* The type might have already been inserted in order to handle
      recursive types.  */
-  gdb_assert (add == NULL || add->gcc_type == gcc_type);
+  if (add != NULL && add->gcc_type != gcc_type)
+    error (_("Unexpected type id from GCC, check you use recent enough GCC."));
 
   if (add == NULL)
     {

gdb/testsuite/ChangeLog

@@ -1,3 +1,12 @@
+2015-07-08  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	PR compile/18484
+	* gdb.compile/compile.c (struct struct_type): Add volatile to
+	selffield's type.
+	* gdb.compile/compile.exp
+	(compile code struct_object.selffield = &struct_object): Skip further
+	struct_object tests if this one xfails.
+
 2015-07-08  Robert O'Callahan  <robert@ocallahan.org>
 
 	PR exp/18617

gdb/testsuite/gdb.compile/compile.c

@@ -42,7 +42,7 @@ struct struct_type {
   float floatfield;
   double doublefield;
   const union union_type *ptrfield;
-  struct struct_type *selffield;
+  volatile struct struct_type *selffield;
   int arrayfield[5];
   _Complex double complexfield;
   _Bool boolfield;

gdb/testsuite/gdb.compile/compile.exp

@@ -189,15 +189,23 @@ gdb_test "p localvar" " = 1"
 # Test setting fields and also many different types.
 #
 
+set skip_struct_object 0
 set test "compile code struct_object.selffield = &struct_object"
 gdb_test_multiple $test $test {
     -re "^$test\r\n$gdb_prompt $" {
 	pass "$test"
     }
-    -re "gdb command line:1:25: warning: assignment discards 'volatile' qualifier from pointer target type \\\[-Wdiscarded-qualifiers\\\]\r\n$gdb_prompt $" {
+    -re " error: Unexpected type id from GCC, check you use recent enough GCC\\.\r\n.*\r\n$gdb_prompt $" {
 	xfail "$test (PR compile/18202)"
+
+	# All following tests will break with the same error message.
+	set skip_struct_object 1
     }
 }
+
+if {$skip_struct_object} {
+    untested "all struct_object tests"
+} else {
     gdb_test "print struct_object.selffield == &struct_object" " = 1"
 
     gdb_test_no_output "compile code struct_object.charfield = 1"
@@ -235,6 +243,8 @@ gdb_test_no_output "compile code struct_object.vectorfield\[2\] = 7"
     gdb_test "print struct_object.vectorfield" \
 	" = \\{0, 0, 7, 0\\}"
 
+}
+
 gdb_test_no_output "compile code union_object.typedeffield = 7"
 gdb_test "print union_object.typedeffield" " = 7"
 gdb_test "print union_object.intfield" " = 7"