I'm reverting one of the changes made to exception.cpp in r151717.  I'm unsure what the change was trying to do, but it didn't do the right thing for __APPLE__.  So instead of trying to guess what was intended, I'm just putting it back the way it was.

llvm-svn: 151727
diff --git a/libcxx/src/exception.cpp b/libcxx/src/exception.cpp
index 92234b2..6b5e698 100644
--- a/libcxx/src/exception.cpp
+++ b/libcxx/src/exception.cpp
@@ -99,6 +99,10 @@
 #if __APPLE__
     // on Darwin, there is a helper function so __cxa_get_globals is private
     return __cxa_uncaught_exception();
+#elif LIBCXXRT
+    __cxa_eh_globals * globals = __cxa_get_globals();
+    return (globals->uncaughtExceptions != 0);
+#else  // __APPLE__
     #warning uncaught_exception not yet implemented
     ::abort();
 #endif  // __APPLE__