in cmake tests let's treat clang like gcc (same options,
same builtins) in many cases.

* don't check the compiler when
  * testing for -fvisibility=hidden support
  * testing for HAVE_ABI_CXA_DEMANGLE
  * testing for HAVE_GCC_ATOMIC_BUILTINS
  * when removing options with string(replace)
  * when running ${CC} --version (ignore the error instead)
* run ABI checks for clang
* use "canonical" gcc flags for clang
* fix groonga too

Also:

* add cmake detection for gcc __atomic_* builtins. they might be
  supported (__ATOMIC_SEQ_CST is defined), but not for all operand
  sizes. In particular, 64-bit atomic load is problematic on i386
* cache check results for Windows
* remove the test for HAVE_CXXABI_H (HAVE_ABI_CXA_DEMANGLE is
  suffifient)