Export ___gxx_personality_v0 as a weak symbol on iOS

This is apparently required by the latest Clang toolchain in order to do a
bitcode build of the engine with LTO enabled.

See https://github.com/flutter/flutter/issues/110140

Change-Id: I6eec2e741e5a9a67aece176aab365303b5425827
Reviewed-on: https://flutter-review.googlesource.com/c/third_party/libcxxabi/+/33360
Reviewed-by: Zach Anderson <zra@google.com>
diff --git a/src/cxa_personality.cpp b/src/cxa_personality.cpp
index b28c58d..98f51c2 100644
--- a/src/cxa_personality.cpp
+++ b/src/cxa_personality.cpp
@@ -905,11 +905,26 @@
         Else a cleanup is not found: return _URC_CONTINUE_UNWIND
+// Flutter: Export __gxx_personality_v0 as a weak symbol on iOS in order to
+// work around an issue with bitcode/LTO builds on the latest Clang toolchain.
+// See https://github.com/flutter/flutter/issues/110140
+// This should no longer be necessary after bitcode support is removed from
+// the Flutter engine.
+#ifdef __APPLE__
+#include <TargetConditionals.h>
+#if defined(TARGET_OS_IOS) && TARGET_OS_IOS
+#define _LIBCXXABI_FUNC_VIS_PERSONALITY __attribute__((visibility("default"))) __attribute__((weak))
 #if !defined(_LIBCXXABI_ARM_EHABI)
 #if defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
 static _Unwind_Reason_Code __gxx_personality_imp
-_LIBCXXABI_FUNC_VIS _Unwind_Reason_Code
 #elif defined(__MVS__)