* Autotools: Refactor AVX-512 checks
- CS synced
- checks wrapped in AC_CACHE_CHECK
- CPP macros PHP_HAVE_AVX512_SUPPORTS and PHP_HAVE_AVX512_VBMI_SUPPORTS
are now either defined to 1 or undefined to avoid manual defining on
Windows (previously they should be either 0 or 1)
* [skip ci] Add basic macros help texts