Log Message:
libatomic_ops: updated to 7.6.12

Changes 7.6.12

Allow to generalize bool-CAS for sparc (gcc)
Declare argument of AO_load_next with const in atomic_ops_stack
Describe double_compare_and_swap operation in README_details
Document CAS operations better in README_details
Fix gcc/sunc x86 AO_compare_double_and_swap_double missing side effect
Fix library name in README_details
Fix link fail caused by missing GCC char/short atomic primitives on riscv64
Fix size of local variable passed to cas[x] (gcc/sparc)
Implement fetch-CAS for sparc (gcc)
Refactor gcc x86 memory constraints
Refine and reformat description of size prefix in README_details
Remove outdated notes in README_details
Replace x86 setz instruction by asm flag output operand (gcc)
Support MSYS host (configure)
Turn off compare_double_and_swap_double_full PIC hack for GCC 5+ (x86)
Update README_win32 to match Makefile.msft
Use GCC atomic intrinsics for s390x (clang 8.0+ and gcc 5.4+)
Use __alignof__ instead of sizeof in atomic variable alignment assertions
Workaround assertion violation in AO_load/store on m68k