While this was useful for local testing while developing the test, it’s
not widely applicable. Look the binary up in the current `${PATH}` if
it’s not specified using `G_TEST_BUILDDIR`.
This is needed to get the `mkenums.py` test working as an
installed-test.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Part of runMkenumsWithHeader() was duplicated in test_reproducible(),
and would otherwise need to be duplicated again in upcoming tests. Many
places duplicated decoding stdout/stderr and checking the exit code.
Introduce a named tuple for the returned fields; and factor out writing
a template file to pass with --template.