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
Also mark debuginfo_tests as UNSUPPORTED if clang can't be found and
remove it from the list of test dependencies if not in
LLVM_ENABLE_PROJECTS.
Differential Revision: https://reviews.llvm.org/D96511
Reviewed by: aprantl
James Henderson