[CMake] Don't set <PROJECT>_STANDALONE_BUILD

We shouldn't be treating runtimes builds as standalone builds since
we have enough of the context loaded into the runtimes environment.

Differential Revision: https://reviews.llvm.org/D57992

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353601 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed