FOLLY_SSSE

Summary: [Folly] `FOLLY_SSSE`, for testing compiler mode support for SSSE3 intrinsics.

Reviewed By: markisaa

Differential Revision: D20414435

fbshipit-source-id: 077a78f880ea8dce44f1aced38a6cca08cdd1f65

folly/Portability.h

@@ -352,6 +352,14 @@ constexpr auto kIsBigEndian = !kIsLittleEndian;
 #endif
 #endif
 
+#ifndef FOLLY_SSSE
+#if defined(__SSSE3__)
+#define FOLLY_SSSE 3
+#else
+#define FOLLY_SSSE 0
+#endif
+#endif
+
 #define FOLLY_SSE_PREREQ(major, minor) \
   (FOLLY_SSE > major || FOLLY_SSE == major && FOLLY_SSE_MINOR >= minor)