Fix 'catch exception' with -flto

A user noticed that when an Ada program (including the runtime) is
compiled with -flto, then "catch exception" does not work -- even
though setting the equivalent breakpoint by hand does work.

Looking into this, it turns out that GCC puts the exception functions
from the Ada runtime into a CU that uses the C language, not Ada.
Then, when trying to look up the relevant symbol,
lookup_name_info::search_name_hash uses the "verbatim" form of the
symbol name (like "<__gnat_debug_raise_exception>") rather than the
"<>"-less form, causing the symbol not to be found.

This patch fixes the problem in two steps.

First, lookup_name_info::search_name_hash is changed to use the same
hack that language_defn::get_symbol_name_matcher uses.  That is, when
the current language is Ada, verbatim-mode lookups are special-cased.
(This is a bit unfortunate; perhaps a better long term approach would
be to promote verbatim mode to a fundamental mode of
lookup_name_info.)

Second, although the above fixes the problem in the Ada language mode,
the code still fails in other languages.  However, due to the way
these lookups are coded in ada-lang.c, I think it makes sense to
temporarily set the current language to Ada in
create_ada_exception_catchpoint.

Tested on x86-64 Fedora 38.

A new test case that mimics the -flto scenario is included.

Reviewed-By: Alexandra Petlanova Hajkova <ahajkova@redhat.com>

gdb/ada-lang.c

@@ -12717,6 +12717,10 @@ create_ada_exception_catchpoint (struct gdbarch *gdbarch,
 				 int enabled,
 				 int from_tty)
 {
+  /* This works around an obscure issue when an Ada program is
+     compiled with LTO.  */
+  scoped_restore_current_language save_language (language_ada);
+
   std::unique_ptr<ada_catchpoint> c
     (new ada_catchpoint (gdbarch, ex_kind,
 			 cond_string.empty () ? nullptr : cond_string.c_str (),