Removed raw references to __APPLE__; now just check to see if it is defined.

llvm-svn: 177297
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: b56e8587aff9d8766a673f51b2d9c525e1535d84
diff --git a/src/stdexcept.cpp b/src/stdexcept.cpp
index 660ebfe..0c4e832 100644
--- a/src/stdexcept.cpp
+++ b/src/stdexcept.cpp
@@ -20,7 +20,7 @@
 #define __has_include(inc) 0
 #endif
 
-#if __APPLE__
+#ifdef __APPLE__
 #include <cxxabi.h>
 #elif defined(LIBCXXRT) || __has_include(<cxxabi.h>)
 #include <cxxabi.h>