Presumbly this will let clang and other compilers use the built-ins as
Notice two changes specifically:
- in _mesa_next_pow_two_64(), always use __builtin_clzll and add a
static assertion that this is safe.
- in macros.h, remove the clang-specific definition since it should
be able to detect __builtin_unreachable in configure.
Reviewed-by: Jason Ekstrand <email@example.com> [C bits]
Reviewed-by: Ian Romanick <firstname.lastname@example.org>