util: no-op __builtin_types_compatible_p() for non-GCC compilers

util: no-op __builtin_types_compatible_p() for non-GCC compilers

__builtin_types_compatible_p() is GCC-specific and breaks the
MSVC build.

This intrinsic has been in u_vector_foreach() for a long time, but
that macro has only recently been used in code
(nir/nir_opt_comparison_pre.c) that's built with MSVC.

Fixes: 2cf59861a ("nir: Add partial redundancy elimination for compares")
Reviewed-by: José Fonseca <jfonseca@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>