this change comprises the in-tree changes required to make use of sccache in gcp.
- a gcp metadata lookup for availability-zone is added to mozconfig, enabling a build to determine its regional gcp sccache bucket
- the sccache cargo build command is modified to include the gcs feature when the environment contains gcs configuration
note that further changes are required on infra to support sccache use. the required changes already exist and are enabled for gcp windows infra, including:
- a json credential file on the build instance filesystem, containing credentials valid for the appropriate scm level bucket for the gcp region
SCCACHE_GCS_KEY_PATH env variable containing the path to the json credential file
SCCACHE_GCS_RW_MODE env variable containg the text
- sccache buckets must exist for each region and scm levels 1 & 3
- credentials for scm level 1 buckets must not be valid for scm level 3 buckets
on gcp systems which do not contain credential files and the above mentioned env variables (eg gecko-[1-3]-b-linux), sccache should fail gracefully without breaking builds.