libc++abi: make __cxa_call_unexpected visible

This may be invoked by the compiler, and needs to be made available so that the
users can reference it.

git-svn-id: svn://svn.chromium.org/llvm-project/libcxxabi/trunk@269255 0b72dbe1-c17f-4bc7-b9db-2b4152be0356
diff --git a/src/cxa_personality.cpp b/src/cxa_personality.cpp
index f3e0aeb..85b6df2 100644
--- a/src/cxa_personality.cpp
+++ b/src/cxa_personality.cpp
@@ -1166,7 +1166,7 @@
 
 
 __attribute__((noreturn))
-void
+_LIBCXXABI_FUNC_VIS void
 __cxa_call_unexpected(void* arg)
 {
     _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(arg);