Fix Windows

Summary: MSVC doesn't support inline assembly.

Reviewed By: yfeldblum, aary

Differential Revision: D10345334

fbshipit-source-id: 5b95d9f6bd8158fe426e01fa176ecfa732cf5bc3

folly/portability/Asm.h

@@ -47,7 +47,9 @@ inline void asm_volatile_pause() {
 }
 
 inline std::uint64_t asm_rdtsc() {
-#if FOLLY_X64
+#if _MSC_VER
+  return (uint64_t)__rdtsc();
+#elif defined(__i386__) || FOLLY_X64
   // read the timestamp counter on x86
   auto hi = std::uint32_t{};
   auto lo = std::uint32_t{};