Fix the lldbinline tests so they make well-formed Makefiles.

lldbinline tests previously did not run correctly unless there was already a
Makefile for them.  This was because the syntax of the emitted Makefile made the
default make rule be the "cleanup" rule, which is pretty unhelpful.  Now the
default rule is the one included from Makefile.rules, which is much better.

llvm-svn: 258763