Otherwise something that ought to seemingly work like `//[x86]
needs-llvm-components: x86` or `//[nll_beyond]should-fail` do not get
evaluated properly.
This is step 2 towards fixing #77548.
In the codegen and codegen-units test suites, the `//` comment markers
were kept in order not to affect any source locations. This is because
these tests cannot be automatically `--bless`ed.
