Consider emitting warnings for incompatible codegen and other command line options

[petrochenkov]

cc #71490 (comment)

For example

• -C relocation-model=ropi doesn't make sense outside of some embedded ARM targets
• -C target-feature=+crt-static is silently ignored on most targets
• -C target-feature=+crt-static is incompatible with -C relocation-model=pic on most targets and +crt-static silently wins (at link time)

Right now rustc behaves more like gcc which silently accepts conflicting options and produces something unspecified, than like clang which tries to produce warnings.
For example, in gcc -shared -pie -pie silently wins, but in clang -shared -pie -shared wins with a warning.

[petrochenkov]

subscribe @Amanieu

[petrochenkov]

This issue is to general, but doesn't try to make specific sub-issues to organize the work.
@workingjubilee and @RalfJung are doing some work in a similar direction, but I don't think it makes sense to keep this issue open.

[RalfJung]

FWIW I am only looking at options that cause soundness issues when used incorrectly, so the ones you mention here are not covered by that.