CI: measure the timing

.gitlab-ci.yml

@@ -5,7 +5,9 @@ lrust-coq8.6:
   # prepare
   - . build/opam-ci.sh 'coq 8.6' 'coq-mathcomp-ssreflect 1.6.1'
   # build
-  - 'time make -j8'
+  - 'time make -j8 TIMED=y 2>&1 | tee build-log.txt'
+  - 'if fgrep Axiom build-log.txt >/dev/null; then exit 1; fi'
+  - 'cat build-log.txt | egrep "[a-zA-Z0-9_/-]+ \(user: [0-9]" | tee build-time.txt'
   cache:
     key: "coq8.6"
     paths:
@@ -13,3 +15,6 @@ lrust-coq8.6:
   only:
   - master
   - ci
+  artifacts:
+    paths:
+    - build-time.txt