Fix build for apple machines.

HAVE_CRASHREPORTERCLIENT_H was potentially undefined and -Wundef is
enabled now.

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@228368 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/abort_message.cpp b/src/abort_message.cpp
index 6d2a5cb..5e25c0f 100644
--- a/src/abort_message.cpp
+++ b/src/abort_message.cpp
@@ -26,7 +26,7 @@
 
 #ifdef __APPLE__
 #   if defined(__has_include) && __has_include(<CrashReporterClient.h>)
-#       define HAVE_CRASHREPORTERCLIENT_H 1
+#       define HAVE_CRASHREPORTERCLIENT_H
 #       include <CrashReporterClient.h>
 #   endif
 #endif
@@ -44,7 +44,7 @@
     va_end(list);
     fprintf(stderr, "\n");
 
-#if defined(__APPLE__) && HAVE_CRASHREPORTERCLIENT_H
+#if defined(__APPLE__) && defined(HAVE_CRASHREPORTERCLIENT_H)
     // record message in crash report
     char* buffer;
     va_list list2;