hmap-test: Skip test instead of reporting success on GCC 4.3.

Commit 1dfc6b1 "hmap-test: Disable tests that GCC 4.3 miscompiles."
disabled some of the hmap-tests, the ones that GCC 4.3 miscompiles.
However, it still reported "success" if the remaining tests succeeded.
John Darrington suggested that reporting that the test was skipped was
more accurate, so this commit does so.