aarch64: Remove alignment assertions [PR109661]

The trunk patch for this PR corrected the ABI for enums that have
a defined underlying type.  We shouldn't change the ABI on the branches
though, so this patch just removes the assertions that highlighed
the problem.

I think the same approach makes sense longer-term: keep the assertions
at maximum strength in trunk, and in any new branches that get cut.
Then, if the assertions trip an ABI problem, fix the problem in trunk
and remove the assertions from active branches.

The tests are the same as for the trunk version, but with all Wpsabi
message and expected output checks removed.

gcc/
	PR target/109661
	* config/aarch64/aarch64.cc (aarch64_function_arg_alignment): Remove
	assertion.
	(aarch64_layout_arg): Likewise.

gcc/testsuite/
	PR target/109661
	* g++.target/aarch64/pr109661-1.C: New test.
	* g++.target/aarch64/pr109661-2.C: Likewise.
	* g++.target/aarch64/pr109661-3.C: Likewise.
	* g++.target/aarch64/pr109661-4.C: Likewise.
	* gcc.target/aarch64/pr109661-1.c: Likewise.