ci: Remove hardcoded CCACHE_DIR in cirrus

This makes it easier to overwrite the value.

Also, drop the dot in the CCACHE_DIR fallback value, because the folder
in the scratch dir does not need and probably should not be hidden.

.cirrus.yml

@@ -4,7 +4,6 @@ env: # Global defaults
  MAKEJOBS: "-j10"
  TEST_RUNNER_PORT_MIN: "14000" # Must be larger than 12321, which is used for the http cache. See https://cirrus-ci.org/guide/writing-tasks/#http-cache
  CI_FAILFAST_TEST_LEAVE_DANGLING: "1" # Cirrus CI does not care about dangling processes and setting this variable avoids killing the CI script itself on error
- CCACHE_DIR: "/tmp/ccache_dir"
 
 # A self-hosted machine(s) can be used via Cirrus CI. It can be configured with
 # multiple users to run tasks in parallel. No sudo permission is required.

ci/test/00_setup_env.sh

@@ -58,7 +58,7 @@ export CCACHE_TEMPDIR=${CCACHE_TEMPDIR:-/tmp/.ccache-temp}
 export CCACHE_COMPRESS=${CCACHE_COMPRESS:-1}
 # The cache dir.
 # This folder exists only on the ci guest, and on the ci host as a volume.
-export CCACHE_DIR=${CCACHE_DIR:-$BASE_SCRATCH_DIR/.ccache}
+export CCACHE_DIR="${CCACHE_DIR:-$BASE_SCRATCH_DIR/ccache}"
 # Folder where the build result is put (bin and lib).
 export BASE_OUTDIR=${BASE_OUTDIR:-$BASE_SCRATCH_DIR/out}
 # The folder for previous release binaries.