llvm-as does everything this test requires, but doesn't depend on a
target being registered. This gets the test passing when
LLVM_DEFAUL_TARGET_TRIPLE is unset.
This patch is related to https://reviews.llvm.org/D100032 which define
some illegal types or operations for x86_amx. There are no arguments,
arrays, pointers, vectors or constants of x86_amx.
Reviewed By: pengfei
Differential Revision: https://reviews.llvm.org/D100472