Fail tests that have a --target compile-flag, but not needs-llvm-components

[nagisa]

Typically when writing a target-specific test, one'll specify a --target compilation flag, but the test will fail when the LLVM does not have the corresponding targets enabled. This is mitigated by telling compiletest that certain llvm components are required in order to run said test. The header looks like this: needs-llvm-components: aarch64.

We should make sure that presence of this annotation is enforced by tidy or compiletest itself when --target flag is used.