This patch adds support to the runtimes build for exposing sub-project targets through the high-level configuration. This will enable exposing the build, check and install targets for sub-project components (i.e. asan, check-asan, install-asan...).
This patch requires minor changes to the runtime projects to take advantage of it, and I'll phase those changes into Compiler-RT shortly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279776 91177308-0d34-0410-b5e6-96231b3b80d8
