Fix typos in 'error' pragma messages

Fix typos in 'error' pragma messages

* src/atomic_ops.h [_HPUX_SOURCE && !__ia64] (AO_barrier_dummy):
Fix typo ("do not") in comment.
* src/atomic_ops/generalize.h [AO_HAVE_nop_acquire]: Fix typo
("do not") in #error message.
* src/atomic_ops/generalize.h [AO_HAVE_nop_release]: Likewise.
* src/atomic_ops/sysdeps/armcc/arm_v6.h [__TARGET_ARCH_ARM < 6]:
Likewise.
* src/atomic_ops/sysdeps/armcc/arm_v6.h [__TARGET_ARCH_ARM < 6]: Add
#error pragma.
* src/atomic_ops_stack.c [AO_HAVE_compare_and_swap_double]: Fix typo
("does not") in #error message.