Only use Clang pragma when compiling with clang.

llvm-svn: 180678
diff --git a/libcxx/src/hash.cpp b/libcxx/src/hash.cpp
index 75e773a..388ab2e 100644
--- a/libcxx/src/hash.cpp
+++ b/libcxx/src/hash.cpp
@@ -12,7 +12,9 @@
 #include "stdexcept"
 #include "type_traits"
 
+#ifdef __clang__
 #pragma clang diagnostic ignored "-Wtautological-constant-out-of-range-compare"
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD