Adjust type of 'flag' and 'tmp' local variables in gcc/arm.h
(code refactoring)

* src/atomic_ops/sysdeps/gcc/arm.h (AO_store,
AO_fetch_compare_and_swap): Change type of "flag" local variable from
AO_t to int (only if AO_BROKEN_TASKSWITCH_CLREX).
* src/atomic_ops/sysdeps/gcc/arm.h (AO_test_and_set, AO_fetch_and_add,
AO_fetch_and_add1, AO_fetch_and_sub1): Change type of "flag" local
variable from unsigned long to int.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_fetch_and_add,
AO_fetch_and_add1, AO_fetch_and_sub1): Change type of "tmp" local
variable from unsigned long to AO_t.
Implement char/short_fetch_and_add for ARMv6+ (GCC)

* src/atomic_ops/sysdeps/gcc/arm.h: Include char_atomic_store.h and
short_atomic_store.h only if not AO_BROKEN_TASKSWITCH_CLREX.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_store): Update comment.
* src/atomic_ops/sysdeps/gcc/arm.h (AO_char_store, AO_short_store):
Implement using LDREXB/STREXB and LDREXH/STREXH, respectively, if
AO_BROKEN_TASKSWITCH_CLREX defined (only if AO_ARM_HAVE_LDREX).
* src/atomic_ops/sysdeps/gcc/arm.h (AO_char_fetch_and_add,
AO_short_fetch_and_add): Implement (based on using LDREXB/STREXB and
LDREXH/STREXH, respectively) if AO_ARM_HAVE_LDREX.