build: Evaluate YAML_LIBS and LZMA_LIBS lazily

No need to check for a package that is only needed for a few targets.

TEST=no more "Package yaml-0.1 was not found in the pkg-config search
path." when emerge'ing sys-boot/coreboot

Change-Id: I56cacea59d9ac13ee3ba587e475e1ff451e535a9
Signed-off-by: Patrick Georgi <>
Commit-Ready: ChromeOS CL Exonerator Bot <>
Tested-by: Patrick Georgi <>
Reviewed-by: Julius Werner <>
1 file changed