Remove newlib header workaround for run_posix_memalign_test.

tests/libc/posix_memalign.c

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 
-/* Newlib currently does not have posix_memalign in its headers, though
- * the malloc implementation (dlmalloc) does support it.
- * http://code.google.com/p/nativeclient/issues/detail?id=2505
- */
-#if defined(NEWLIB)
-extern int posix_memalign(void **memptr, size_t alignment, size_t size);
-#endif
-
 int main(int argc, char* argv[]) {
   char *outp;
   /* Try a few alignments, some of them might be the standard malloc align.
    * They should all be powers of 2 and be a multiple of sizeof(void*).
    */
   size_t align_to_test[] = {4, 8, 16, 32, 64, 128, 256, 512, 1024, 0};
   size_t sizes_to_test[] = {1, 2, 4, 8, 10, 16, 32, 64, 128, 256, 512, 1024, 0};
   int i = 0;
   int j = 0;
 
@@ skipping 30 matching lines @@
 
   /* Check that smaller than sizeof(void*) alignment fails. */
   if (posix_memalign((void**)&outp, sizeof(void*) - 1,
                      20 * sizeof(char)) != EINVAL) {
     fprintf(stderr, "posix_memaligned failed to return EINVAL for non-pow2!\n");
     return 1;
   }
 
   return 0;
 }