sstatesig: Allow to cross target-native/cross/nativesdk boundary

:Release Notes:
We want to make sstate signatures even more strict to rebuild target
recipes when their native dependencies are changed.

:Detailed Notes:
Backport useful changes from latest oe-core as well.

:Testing Performed:
Only build tested and verified with bitbake-diffsigs +
sstate-diff-machine.sh.

:QA Notes:
No change to image.

:Build Notes:
Invalidates almost all sstate signatures.

:Issues Addressed:
[GF-51950] Build doesn't recognize bbappend-ed
           cmake-modules-webos-native as having changed

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I10e7ba96cd4639918e013e200e836a8a39a23bcc
Reviewed-on: https://g2g.palm.com/4267
Reviewed-by: DCO Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>