[runtimes] Create check- targets for LLVM_RUNTIME_DISTRIBUTION_COMPONENTS

The sub-component check targets won't be automatically created until the
runtime configurations have run (and the main LLVM configure has rerun
afterwards). Work around this by creating check- targets for components
in LLVM_RUNTIME_DISTRIBUTION_COMPONENTS as well (and making sure they
get the proper test dependencies).

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D138967