libcompiler_rt: move file list to Makefile.inc for reuse elsewhere

[emaste]

Summary

This should be a no-op change, but allows other, future components to #include ../libcompiler_rt/Makefile.inc to pick up the compiler-rt functions.

[dim]

What kind of elsewhere are you thinking about? :) (I also need to merge this to the clang390-import branch, where I did a little bit of remodeling in all the llvm project related Makefiles...)

[emaste]

Update Makefile.inc to match style of libcompiler_rt Makefile in upcoming clang390 import branch

[dim]

LGTM then.