[PATCH v2] Revert __HAVE_64B_ATOMICS configure check

[Wilco Dijkstra]

Hi Maciej,

> AFAICT in the __HAVE_64B_ATOMICS == 1 case `sem_t' includes a `uint64_t'
> member, so the structure will have 64-bit alignment on the MIPS target.

sysdeps/mips/nptl/bits/semaphore.h has:

typedef union
{
  char __size[__SIZEOF_SEM_T];
  long int __align;
} sem_t;

Even if __SIZEOF_SEM_T is like the 64-bit ABI, the alignment will be 4 and
so it can't use 64-bit atomics on this structure.

Cheers,
Wilco