Define AO_nop_full as compiler barrier for pre-ARMv6 single-core case

* src/atomic_ops/sysdeps/gcc/arm.h (AO_nop_full): Define for pre-ARMv6
as well (as a compiler barrier) if AO_UNIPROCESSOR; refine comment.
* src/atomic_ops/sysdeps/msftc/arm.h (AO_nop_full): Likewise.
* src/atomic_ops/sysdeps/msftc/arm.h: Eliminate duplicated include of
test_and_set_t_is_ao_t.h.
Implement load/store via simple LDR/STR for ARMv6+ (msftc)

* src/atomic_ops/sysdeps/msftc/arm.h: Include
all_aligned_atomic_load_store.h instead of all_atomic_load_store.h
(since unaligned accesses are not guaranteed to be atomic).
* src/atomic_ops/sysdeps/msftc/arm.h (AO_load): Remove; include
all_aligned_atomic_load_store.h unconditionally instead (thus
implementing AO[_char/short]_load/store via simple LDR/STR; add
comment about Windows interrupt handlers.
* src/atomic_ops/sysdeps/msftc/arm.h: Add TODO item to implement
AO_test_and_set_full (for pre-ARMv6).
Revert "Fix read_ordered.h inclusion for ARM"
(because it makes load_acquire/read incorrect for multi-core ARM)

This reverts commit fcc838be49c98486c26738764f895d34de0716be.
Fix (remove) invalid include of read_ordered.h for ARM
(fix commit 2df9c1e partially)

* src/atomic_ops/sysdeps/gcc/arm.h: Do not include read_ordered.h
(because load_acquire should contain a DMB instruction in a multi-core
case, new load_acquire/read primitives implementation is generalized
using nop_full/read which either contain a DMB instruction, or is just
a compiler barrier for uniprocessor).
* src/atomic_ops/sysdeps/armcc/arm_v6.h: Likewise.
* src/atomic_ops/sysdeps/msftc/arm.h: Likewise.
Add compile-time assertion for size of 'standard' AO_double_t

* src/atomic_ops/sysdeps/standard_ao_double_t.h
(AO_double_t_size_static_assert): Add compile-time assertion for
AO_double_t size.
Implement AO_and/or/xor efficiently for ARM

* src/atomic_ops/sysdeps/gcc/arm.h (AO_and, AO_or, AO_xor): Implement
directly using LDREX/STREX (enabled only if not AO_PREFER_GENERALIZED).