restrict availability on 32-bit platforms

Summary:
Restrict F14 availability (and use the fallback version) on 32-bit platforms
until we audit the code, removing assumptions such as `size_t` is 64-bit and
finding a mixer that does not require `__int128`.

Reviewed By: nbronson

Differential Revision: D8525351

fbshipit-source-id: 54fce48fe94235c8525074216426cf254db26b4e

folly/container/detail/F14IntrinsicsAvailability.h

@@ -19,14 +19,14 @@
 #include <folly/Portability.h>
 
 // clang-format off
-// F14 has been implemented for SSE2 and AARCH64 NEON (so far)
+// F14 has been implemented for x86_64 SSE2 and AARCH64 NEON (so far)
 #ifndef FOLLY_F14_VECTOR_INTRINSICS_AVAILABLE
-# if FOLLY_SSE >= 2 || FOLLY_AARCH64
+# if FOLLY_SSE >= 2 && FOLLY_X64 || FOLLY_AARCH64
 #  define FOLLY_F14_VECTOR_INTRINSICS_AVAILABLE 1
 # else
 #  define FOLLY_F14_VECTOR_INTRINSICS_AVAILABLE 0
-#  pragma message                                       \
-    "Vector intrinsics unavailable on this platform, "  \
+#  pragma message                                                     \
+    "Vector intrinsics / F14 support unavailable on this platform, "  \
     "falling back to std::unordered_map / set"
 # endif
 #endif