Cut FOLLY_HAVE_MEMRCHR

Summary: [Folly] Cut `FOLLY_HAVE_MEMRCHR` since it is now unused.

Reviewed By: Orvid

Differential Revision: D22130149

fbshipit-source-id: b10c5a52354f5c549d96b54e0c165f08b96612b1

CMake/FollyConfigChecks.cmake

@@ -85,9 +85,6 @@ string(REGEX REPLACE
 
 check_symbol_exists(pthread_atfork pthread.h FOLLY_HAVE_PTHREAD_ATFORK)
 
-# Unfortunately check_symbol_exists() does not work for memrchr():
-# it fails complaining that there are multiple overloaded versions of memrchr()
-check_function_exists(memrchr FOLLY_HAVE_MEMRCHR)
 check_symbol_exists(accept4 sys/socket.h FOLLY_HAVE_ACCEPT4)
 check_symbol_exists(getrandom sys/random.h FOLLY_HAVE_GETRANDOM)
 check_symbol_exists(preadv sys/uio.h FOLLY_HAVE_PREADV)

CMake/folly-config.h.cmake

@@ -42,7 +42,6 @@
 #include <features.h>
 #endif
 
-#cmakedefine FOLLY_HAVE_MEMRCHR 1
 #cmakedefine FOLLY_HAVE_ACCEPT4 1
 #cmakedefine01 FOLLY_HAVE_GETRANDOM
 #cmakedefine FOLLY_HAVE_PREADV 1