Fix windows build errors (rdtsc and fnptr) (#12008)

Summary:
Combining best parts of https://github.com/facebook/rocksdb/issues/11794 and https://github.com/facebook/rocksdb/issues/11766, fixing the CircleCI config in the latter. I was going to amend the latter but wasn't granted access.

Ideally this would be ported back to 8.4 branch and crc32c part into 8.3 branch.

BACKPORT NOTE: removed CircleCI config changes from this diff as they
depend (at least superficially) on changes not in this branch.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12008

Test Plan: CI

Reviewed By: hx235

Differential Revision: D50616172

Pulled By: pdillinger

fbshipit-source-id: fa7f778bc281e881a140522e774f480c6d1e5f48

env/unique_id_gen.cc

@@ -21,6 +21,7 @@
 #ifdef __SSE4_2__
 #ifdef _WIN32
 #include <intrin.h>
+#define _rdtsc() __rdtsc()
 #else
 #include <x86intrin.h>
 #endif

util/crc32c.cc

@@ -1117,7 +1117,13 @@ static inline Function Choose_Extend() {
   }
 #elif defined(__SSE4_2__) && defined(__PCLMUL__) && !defined NO_THREEWAY_CRC32C
   // NOTE: runtime detection no longer supported on x86
-  (void)ExtendImpl<DefaultCRC32>;  // suppress unused warning
+#ifdef _MSC_VER
+#pragma warning(disable: 4551)
+#endif
+  (void)ExtendImpl<DefaultCRC32>; // suppress unused warning
+#ifdef _MSC_VER
+#pragma warning(default: 4551)
+#endif
   return crc32c_3way;
 #else
   return ExtendImpl<DefaultCRC32>;