+ Rename test script to run-lit-tests and move to libexec to match
llvm-test.
+ Move most of the configuration out of the spec file and into the
test script and a custom lit config file.
+ Stop testing libomp with gcc. Most of the complication in the
spec file was to enable testing with gcc. A user would have to
go way out of their way to make libomp work with gcc, so I don't
think there is much value in keeping the complexity in order to test
this.
