Only use Clang pragma when compiling with clang.

llvm-svn: 180678
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: ff3ce2bdc060ddddf358b054b819b1e762e69c2f
diff --git a/src/hash.cpp b/src/hash.cpp
index 75e773a..388ab2e 100644
--- a/src/hash.cpp
+++ b/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