Revert "hardening: Disable GCC randstruct for COMPILE_TEST"
This reverts commit f5c68a4e84f9feca3be578199ec648b676db2030.
It is again possible to build "allmodconfig" with the randstruct GCC
plugin, so enable it for COMPILE_TEST to catch future bugs.
Signed-off-by: Kees Cook <kees@kernel.org>