For "Debug" and "Release" builds, don't build llvm into the $(OBJROOT) since

we often nuke our "build" folder so we can do clean builds. This way if you
are building your own LLVM you won't have to rebuild LLVM when you do remove
your build folder. The new location for the LLVM build is:

lldb/llvm-build

llvm-svn: 143713