[ORC] Add some more basic sanity tests for the LLJIT.
minimal.ll contains a main function that returns zero, and
single-function-call.ll contains a main function that calls a foo function that
returns zero. These minimal tests can help to rule out some trivial JIT bugs
when other tests fail.
This commit also renames hello.ll to global-ctors-and-dtors.ll, which better
reflects what it is actually testing.