kselftest/arm64: Enable build of PAC tests with LLVM=1

Currently we don't build the PAC selftests when building with LLVM=1 since
we attempt to test for PAC support in the toolchain before we've set up the
build system to point at LLVM in lib.mk, which has to be one of the last
things in the Makefile.

Since all versions of LLVM supported for use with the kernel have PAC
support we can just sidestep the issue by just assuming PAC is there when
doing a LLVM=1 build.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241111-arm64-selftest-pac-clang-v1-1-08599ceee418@kernel.org


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>