selftest/x86/signal: Include test cases for validating sigaltstack

The test measures the kernel's signal delivery with different (enough vs.
insufficient) stack sizes.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Len Brown <len.brown@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20210518200320.17239-7-chang.seok.bae@intel.com