Prevent load_acquire redefinition in ordered_loads_only.h

* src/atomic_ops/sysdeps/loadstore/ordered_loads_only.template
(AO_XSIZE_load_acquire, AO_HAVE_XSIZE_load_acquire): Do not define
if AO_HAVE_XSIZE_load_acquire already defined.
* src/atomic_ops/sysdeps/loadstore/ordered_loads_only.h: Regenerate.
Implement char/short_load primitives for ARMv6+

* src/atomic_ops/sysdeps/armcc/arm_v6.h: Include all_atomic_only_load.h
(with defined AO_ACCESS_CHECK_ALIGNED, AO_ACCESS_short_CHECK_ALIGNED
and AO_ACCESS_int_CHECK_ALIGNED).
* src/atomic_ops/sysdeps/gcc/arm.h: Likewise.
* src/atomic_ops/sysdeps/armcc/arm_v6.h (AO_load, AO_HAVE_load):
Remove (since defined by all_atomic_only_load.h).
* src/atomic_ops/sysdeps/gcc/arm.h (AO_load, AO_HAVE_load): Likewise.
* src/atomic_ops/sysdeps/gcc/arm.h: Adjust atomic_store.h filename in
comment.
Implement double_store for ARMv7 using LDREXD/STREXD

* src/atomic_ops/sysdeps/gcc/arm.h (AO_nop_full, AO_nop_write,
AO_double_load, AO_double_compare_and_swap): Add comment about missing
AO_THUMB_GO_ARM.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_double_load): Add comment.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_double_store): New primitive
(implemented directly using LDREXD/STREXD).
.gitignore: Ignore .gch files