livepatch/klp-build: improve short-circuit validation

livepatch/klp-build: improve short-circuit validation

Update SHORT_CIRCUIT behavior to better handle patch validation and
argument processing in later klp-build steps.

Perform patch validation for both step 1 (building original kernel) and
step 2 (building patched kernel) to ensure patches are verified before
any compilation occurs.

Additionally, allow the user to omit input patches when skipping past
step 2.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Link: https://patch.msgid.link/20260310203751.1479229-9-joe.lawrence@redhat.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>