aarch64: disable LIB32 with gcc

gcc doesn't have -m32 support on aarch64 so mark LIB32 broken there.

We have to check both COMPILER_TYPE and X_COMPILER_TYPE becuase
X_COMPILER_TYPE is only conditionally set and COMPILER_TYPE is the host
compiler in Makefile.inc1.

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D45089