I observed an error in BuildPackages which result in failure to build some libraries:

media-libs/cros-camera-libcbm-0.0.1-r128
media-libs/cros-camera-libcamera_metadata-0.0.1-r95
media-libs/cros-camera-libcamera_exif-0.0.1-r127
media-libs/cros-camera-libcamera_common-0.0.1-r129
media-libs/cros-camera-libcamera_v4l2_device-0.0.1-r105
media-libs/cros-camera-libcamera_timezone-0.0.1-r127

I looked at the log and found the first error reported was something like:
 
cros-camera-libcamera_metadata-0.0.1-r95: ../../../../../../../tmp/portage/media-libs/cros-camera-libcamera_metadata-0.0.1-r95/work/cros-camera-libcamera_metadata-0.0.1/camera/android/libcamera_metadata/src/camera_metadata.c:26:10: fatal error: 'system/camera_metadata.h' file not found

This is observed on a llvm-next tryjob of nautilus-release for nightly tests. And it was not the issue for release builders.

Full log is here:
https://luci-logdog.appspot.com/logs/chromeos/buildbucket/cr-buildbucket.appspot.com/8924731714275083664/+/steps/BuildPackages__afdo_use_/0/stdout?format=raw