Fix build on 32-bit platforms

Summary: This fixes a compile error on 32-bit platforms.

Reviewed By: Orvid

Differential Revision: D8147916

fbshipit-source-id: 86b66b684bed5ffb262630a361cf239948b8bb97

folly/hash/detail/Crc32cDetail.cpp

@@ -42,7 +42,7 @@
 namespace folly {
 namespace detail {
 
-#if FOLLY_SSE_PREREQ(4, 2)
+#if defined(FOLLY_X64) && FOLLY_SSE_PREREQ(4, 2)
 
 namespace crc32_detail {