[cross-project-tests] Add/update check-* targets for cross-project-tests

This change modifies the existing check-debuginfo target to only run the
debuginfo tests within the cross-project-tests, and adds a new target
(check-cross-project) which runs all the tests. The former has also been
modified to not be included in check-all (since the check-cross-project
target covers them).

Differential Revision: https://reviews.llvm.org/D96513

Reviewed by: aprantl