port_posix: use posix_memalign() for aligned_alloc

Summary:
to workaround issue of http://tracker.ceph.com/issues/21422 .
and in tcmalloc aligned_alloc and posix_memalign() are basically the
same thing. the same applies to GNU glibc.

fixes #3175

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
Closes https://github.com/facebook/rocksdb/pull/3862

Differential Revision: D8147930

Pulled By: yiwu-arbug

fbshipit-source-id: 355afe93c4dd0a96a0d711ef190e8b86fbe8d11d

port/port_posix.cc

@@ -188,8 +188,6 @@ int GetMaxOpenFiles() {
 void *cacheline_aligned_alloc(size_t size) {
 #if __GNUC__ < 5 && defined(__SANITIZE_ADDRESS__)
   return malloc(size);
-#elif defined(_ISOC11_SOURCE)
-  return aligned_alloc(CACHE_LINE_SIZE, size);
 #elif ( _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600 || defined(__APPLE__))
   void *m;
   errno = posix_memalign(&m, CACHE_LINE_SIZE, size);