The report generation was broken by the split of the various test units;
also, we were using GTest in a way that's not really sanctioned by
upstream.
This commit tries to re-use the targets from GLib's Makefile rules while
compensating for our own set up.
Instead of asking gtester to run ./test-conformance directly we now tell
it to run a list of wrapper scripts. This results in each test being
spawned in a separate process avoiding leakage of state between tests
which has been a big problem with the conformance tests for quite a
while now.