core: send code coverage only with gcc, not with clang

.travis.yml

@@ -1,12 +1,11 @@
+dist: xenial
+sudo: required
 language: c
 
 compiler:
     - gcc
     - clang
 
-sudo: required
-dist: xenial
-
 env:
     - BUILDTOOL="cmake" BUILDARGS=""
     # - BUILDTOOL="cmake" BUILDARGS="-DENABLE_PYTHON3=ON"
@@ -16,6 +15,12 @@ env:
     # - BUILDTOOL="autotools" BUILDARGS="--enable-python3"
     - BUILDTOOL="autotools" BUILDARGS="--disable-gnutls"
 
+matrix:
+    fast_finish: true
+    exclude:
+      - compiler: clang
+        env: BUILDTOOL="cmake" BUILDARGS="-DENABLE_CODE_COVERAGE=ON" CODECOVERAGE="1"
+
 before_script:
     # Workaround https://github.com/travis-ci/travis-ci/issues/5326
     - export PATH=$(echo $PATH | tr ':' "\n" | sed '/\/opt\/python/d' | tr "\n" ":" | sed "s|::|:|g")
@@ -44,6 +49,3 @@ after_success:
     - weechat --version
     - weechat --temp-dir --run-command "/debug dirs;/debug libs" --run-command "/quit"
     - if [ "$CODECOVERAGE" = "1" ]; then bash <(curl -s https://codecov.io/bash) -f coverage.info || echo "Codecov error"; fi
-
-matrix:
-    fast_finish: true