The tests below are not actually invalid, they cause the compiler to emit only
warnings and properly belong in the warnings directory.
tests/invalid/empty_interface.{m,err_exp}:
tests/invalid/foreign_singleton.{m,err_exp}:
tests/invalid/obsolete_proc_pragma.{m,err_exp}:
Shift these tests into the warnings directory and use the
appropriate extension for expected outputs in that directory
tests/invalid/Mmakefile:
tests/invalid/Mercury.options:
tests/warnings/Mercury.options:
tests/warnings/Mmakefile:
Conform to the above changes.
