Reapply "llvm-mt: implement simple merging of manifests, not factoring namespaces.

This time with correct #if.

This reverts commit 9cf4eca0e0383040c1ff1416815c7f649650c2a0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309064 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed