perf symbol-elf: Avoid a weak cxx_demangle_sym function

cxx_demangle_sym is weak in case demangle-cxx.c replaces the
definition in symbol-elf.c. When demangle-cxx.c is built
HAVE_CXA_DEMANGLE_SUPPORT is defined, as such the define can be used
to avoid a weak symbol.

As weak symbols are outside of the C standard their use can lead to
strange behaviors, in particular with LTO, as well as causing issues to
be hidden at link time.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241119031754.1021858-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -287,8 +287,9 @@ static bool want_demangle(bool is_kernel_sym)
  * Demangle C++ function signature, typically replaced by demangle-cxx.cpp
  * version.
  */
-__weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
-			      bool modifiers __maybe_unused)
+#ifndef HAVE_CXA_DEMANGLE_SUPPORT
+char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
+		       bool modifiers __maybe_unused)
 {
 #ifdef HAVE_LIBBFD_SUPPORT
 	int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
@@ -302,6 +303,7 @@ __weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __mayb
 	return NULL;
 #endif
 }
+#endif /* !HAVE_CXA_DEMANGLE_SUPPORT */
 
 static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 {