Log Message:
libatomic_ops: updated to 7.6.6

7.6.6:
COPYING: sync with FSF's gpl-2.0.txt
Fix 'undefined reference to __atomic_load/store/cas_16' error (gcc-7/x64)
Fix a typo in the overview section of README
Fix comments style in configure.ac and Makefile.am
Update copyright information in README and some header files