make data pointers volatile so that memory zeroing won't get optimised away

--HG--
branch : libtomcrypt
extra : convert_revision : fa68f28b581de8ed5f2af8f1ab95b33bcf4a7e18

zeromem.c

@@ -12,7 +12,7 @@
 
 void zeromem(void *dst, size_t len)
 {
- unsigned char *mem = (unsigned char *)dst;
+ volatile unsigned char *mem = (unsigned char *)dst;
  _ARGCHK(dst != NULL);
  while (len-- > 0)
     *mem++ = 0;