* sysdeps/i386/i486/bits/atomic.h (atomic_bit_set): Use "ir"
constraint to permit non-constant BIT argument.
(atomic_bit_test_set): Likewise.
* sysdeps/x86_64/bits/atomic.h (atomic_bit_test_set): Likewise.
(atomic_bit_set): Likewise. Use 1UL in case that BIT might be >= 32.
For quadword case, use "i" constraint if __builtin_constant_p and < 32
or "r" constraint otherwise.