Revert "fortify: Allow KUnit test to build without FORTIFY"

Revert "fortify: Allow KUnit test to build without FORTIFY"

This reverts commit a9dc8d0442294b426b1ebd4ec6097c82ebe282e0.

The standard for KUnit is to not build tests at all when required
functionality is missing, rather than doing test "skip". Restore this
for the fortify tests, so that architectures without
CONFIG_ARCH_HAS_FORTIFY_SOURCE do not emit unsolvable warnings.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Closes: https://lore.kernel.org/all/CAMuHMdUrxOEroHVUt7-mAnKSBjY=a-D3jr+XiAifuwv06Ob9Pw@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>