[gdb/build] Use -fno-hoist-adjacent-loads for gcc <= 13

When building gdb with gcc 12 and -fsanitize=threads while renabling
background dwarf reading by setting dwarf_synchronous to false, I run into:
...
(gdb) file amd64-watchpoint-downgrade
Reading symbols from amd64-watchpoint-downgrade...
(gdb) watch global_var
==================
WARNING: ThreadSanitizer: data race (pid=20124)
  Read of size 8 at 0x7b80000500d8 by main thread:
    #0 cooked_index_entry::full_name(obstack*, bool) const cooked-index.c:220
    #1 cooked_index::get_main_name(obstack*, language*) const cooked-index.c:735
    #2 cooked_index_worker::wait(cooked_state, bool) cooked-index.c:559
    #3 cooked_index::wait(cooked_state, bool) cooked-index.c:631
    #4 cooked_index_functions::wait(objfile*, bool) cooked-index.h:729
    #5 cooked_index_functions::compute_main_name(objfile*) cooked-index.h:806
    #6 objfile::compute_main_name() symfile-debug.c:461
    #7 find_main_name symtab.c:6503
    #8 main_language() symtab.c:6608
    #9 set_initial_language_callback symfile.c:1634
    #10 get_current_language() language.c:96
    ...

  Previous write of size 8 at 0x7b80000500d8 by thread T1:
    #0 cooked_index_shard::finalize(parent_map_map const*) \
         dwarf2/cooked-index.c:409
    #1 operator() cooked-index.c:663
    ...

  ...

SUMMARY: ThreadSanitizer: data race cooked-index.c:220 in \
  cooked_index_entry::full_name(obstack*, bool) const
==================
Hardware watchpoint 1: global_var
(gdb) PASS: gdb.arch/amd64-watchpoint-downgrade.exp: watch global_var
...

This was also reported in PR31715.

This is due do gcc PR110799 [1], generating wrong code with
-fhoist-adjacent-loads, and causing a false positive for
-fsanitize=threads.

Work around the gcc PR by forcing -fno-hoist-adjacent-loads for gcc <= 13
and -fsanitize=threads.

Tested in that same configuration on x86_64-linux.  Remaining ThreadSanitizer
problems are the ones reported in PR31626 (gdb.rust/dwindex.exp) and
PR32247 (gdb.trace/basic-libipa.exp).

PR gdb/31715
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31715

Tested-By: Bernd Edlinger <[email protected]>
Approved-By: Tom Tromey <[email protected]>

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110799

gdbsupport/common-defs.h

@@ -20,6 +20,13 @@
 #ifndef COMMON_COMMON_DEFS_H
 #define COMMON_COMMON_DEFS_H
 
+#if defined (__SANITIZE_THREAD__) && defined (__GNUC__) \
+  && !defined (__clang__) && __GNUC__ <= 13
+
+/* Work around PR gcc/110799.  */
+#pragma GCC optimize("-fno-hoist-adjacent-loads")
+#endif
+
 #include <gdbsupport/config.h>
 
 #undef PACKAGE_NAME