[CMake] Include runtimes test suites in check-all

Prior to this change, we would make check-all depend on check-runtimes
which is a target that runs tests in the runtimes build. This means that
the runtimes tests are going to run prior to other test suites in
check-all, and if one of them fails, we won't run the other test suites
at all.

To address this issue, we instead collect the list of test suites and
their dependencies from the runtimes subbuild, and include them in
check-all, so a failure of runtimes test suite doesn't prevent other
test suites from being executed.

This addresses https://github.com/llvm/llvm-project/issues/54154.

Differential Revision: https://reviews.llvm.org/D121276