Put ccache dirs in build dir to avoid dirty worktree

Placing these directories at the root will make the git revision
detection consider the working directory to be dirty.

.gitlab/ci/templates/srb2ci.yml

@@ -2,13 +2,13 @@
   image: git.do.srb2.org:5050/stjr/srb2ci/srb2ci:stable
 
   cache:
-    - key: ccache-$CI_PROJECT_PATH_SLUG-$CI_JOB_NAME_SLUG
+    - key: ccache-$CI_JOB_NAME_SLUG-$CI_COMMIT_REF_SLUG
       fallback_keys:
-        - cache-$CI_PROJECT_PATH_SLUG-$CI_DEFAULT_BRANCH
-        - cache-$CI_PROJECT_PATH_SLUG-default
+        - ccache-$CI_JOB_NAME_SLUG-$CI_DEFAULT_BRANCH
+        - ccache-$CI_JOB_NAME_SLUG-master
       paths:
-        - ccache
-        - ccache_statslog
+        - build/ccache
+        - build/ccache_statslog
 
     - key: apt-$CI_JOB_IMAGE
       paths:
@@ -100,19 +100,19 @@
           echo Adding ccache configution option
       - |
           # base_dir
-          echo base_dir = $PWD                  | tee --append ~/.ccache/ccache.conf
+          echo base_dir = $CI_PROJECT_DIR                        | tee --append ~/.ccache/ccache.conf
       - |
           # cache_dir
-          echo cache_dir = $PWD/ccache          | tee --append ~/.ccache/ccache.conf
+          echo cache_dir = $CI_PROJECT_DIR/build/ccache          | tee --append ~/.ccache/ccache.conf
       - |
           # compiler_check
-          echo compiler_check = content         | tee --append ~/.ccache/ccache.conf
+          echo compiler_check = content                          | tee --append ~/.ccache/ccache.conf
       - |
           # stats_log
-          echo stats_log = $PWD/ccache_statslog | tee --append ~/.ccache/ccache.conf
+          echo stats_log = $CI_PROJECT_DIR/build/ccache_statslog | tee --append ~/.ccache/ccache.conf
       - |
           # max_size
-          echo max_size = 300M                  | tee --append ~/.ccache/ccache.conf
+          echo max_size = 300M                                   | tee --append ~/.ccache/ccache.conf
       - |
           # ccache_config
           echo -e "\e[0Ksection_end:`date +%s`:ccache_config\r\e[0K"