gccrs: Add new checks for `#[repr(align)]` attribute

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-base.cc (TypeCheckBase::parse_repr_options): New
	check for `#[repr(align)]` to enforce having a parameter that is a power of 2.

gcc/testsuite/ChangeLog:

	* rust/compile/invalid_repr_hint.rs: Update existing and add new `align` test cases.

Signed-Off-By: Yap Zhi Heng <yapzhhg@gmail.com>