Enable llgs to build against experimental Android AOSP lldb/llvm/clang/compiler-rt repos.

See http://reviews.llvm.org/D5495 for more details.

These are changes that are part of an effort to support building llgs, within the AOSP source tree, using the Android.mk
build system, when using the llvm/clang/lldb git repos from AOSP replaced with the experimental ones currently in
github.com/tfiala/aosp-{llvm,clang,lldb,compiler-rt}.