Generalize compare_double_and_swap_double using double_compare_and_swap

Generalize compare_double_and_swap_double using double_compare_and_swap

* src/atomic_ops/generalize.h (AO_compare_double_and_swap_double,
AO_compare_double_and_swap_double_full): New inline function (move
code from gcc/arm.h and msftc/x86.h) based on the corresponding
double_compare_and_swap (only if AO_HAVE_DOUBLE_PTR_STORAGE and
AO_HAVE_double_compare_and_swap[_full] defined but not
AO_HAVE_compare_double_and_swap_double[_full]).
* src/atomic_ops/generalize.h (AO_HAVE_compare_double_and_swap_double,
AO_HAVE_compare_double_and_swap_double_full): New macro (moved
from gcc/arm.h and msftc/x86.h, respectively).
* src/atomic_ops/sysdeps/gcc/arm.h
(AO_compare_double_and_swap_double): Remove definition from this file;
remove TODO item.
* src/atomic_ops/sysdeps/msftc/x86.h
(AO_compare_double_and_swap_double_full): Likewise.