This patch allows for linking selected files with system libc. This allows for creating libraries interacting with filesystem, standard I/O and other parts of system. Until now it was only possible using CMocka proxy functions or functions not masked by code under test. Signed-off-by: Jakub Czapiga <jacz@semihalf.com> Change-Id: I652362ba61a25e974d706357fc36479ccee763e4 Reviewed-on: https://review.coreboot.org/c/coreboot/+/70108 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Jan Dabros <jsd@semihalf.com>