Fix issue with clang build on Windows

Summary:
Matches logic on L83 where we check both _MSC_VER and __clang__

We need to add this check to avoid suppressing the useful pedantic warnings in //xplat/js/react-native-github.

Reviewed By: shwanton, Orvid

Differential Revision: D52603274

fbshipit-source-id: 02c146b141c8795c3ea3c5cb6984b6dfedd9c10a

Author: rozele

third-party/folly/src/folly/lang/Pretty.h

@@ -86,7 +86,7 @@ using pretty_default_tag = std::conditional_t< //
 
 template <typename T>
 static constexpr auto pretty_raw(pretty_tag_msc) {
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
   return pretty_carray_from(__FUNCSIG__);
 #endif
 }