build system: generalize src-to-obj

It can now be used on any list of files instead of assuming
to work on $($(class)-src).

This is inspired by the commit listed below, but rewritten to match
upstream, and split in smaller pieces to keep intent clear.

Change-Id: Ib77afedd4c3f847963497beea503f5447a7c6e28
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Based-On-Change-Id: I50af7dacf616e0f8ff4c43f4acc679089ad7022b
Based-On-Signed-off-by: Julius Werner <jwerner@chromium.org>
Based-On-Reviewed-on: https://chromium-review.googlesource.com/219170
Reviewed-on: http://review.coreboot.org/9161
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
1 file changed