Verify llvm-needs-components are not empty and match the --target value

[dpaoliello]

I recently discovered a test with an empty llvm-needs-components entry (fixed in rust-lang/rust#149178) which meant that it didn't work correctly when building Rust with a limited set of LLVM targets.

This change makes a pair of improvements to prevent this issue from creeping in again:

• When parsing directives with values, compiletest will now raise an error if there is an empty value.
• Improved the target_specific_tests tidy checker to map targets to LLVM components, to verify that any existing llvm-needs-components contains the target being used.

I also fixed all the issues flagged by the improved tidy checker.

[rustbot]

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[rustbot]

Some changes occurred in tests/codegen/sanitizer

cc @rcvalle

There are changes to the tidy tool.

cc @jieyouxu

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[jieyouxu]

r? jieyouxu