malloca, freea are not thread-safe

[Florian Weimer]

The mmalloca function used to implement malloca accesses a static global 
array without synchronization:

#define HASH_TABLE_SIZE 257
static void * mmalloca_results[HASH_TABLE_SIZE];
…
mmalloca (size_t n)
{
…
    /* Enter p into the hash table.  */
          slot = (uintptr_t) p % HASH_TABLE_SIZE;
          h->next = mmalloca_results[slot];
          mmalloca_results[slot] = p;
freea also causes valgrind warnings because it contains an out-of-bounds 
access.  This is very undesirable because it will cause programmers to 
miss real bugs.

This code has been copied into libunistring and results in a thread 
safety hazard there.

Thanks,
Florian