hmap-test: Disable tests that GCC 4.3 miscompiles.

Commit ac58b3c51 "Avoid bug in GCC 4.3 in hmap-test." attempted to work
around a bug in GCC 4.3 that was causing test failures in hmap-test.
Unfortunately, the problem has started resurfacing again, probably due to
changes elsewhere, so this commit simply disables the tests in question
when PSPP is built with GCC 4.3.