ci: enable code coverage

Change-Id: I1fb68bc05b1a4a75c249a11c87fd6139c1700e75
diff --git a/.travis.yml b/.travis.yml
index aae985f..37330c3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,6 +24,7 @@
     - env: COMPILER=clang++-8
     - env: COMPILER=clang++-10
     - env: COMPILER=clang++-11
+    - env: COMPILER=clang++-12
 
     # macOS
     - os: osx
@@ -47,7 +48,7 @@
 
   allow_failures:
     - arch: s390x # bug 4818
-    - env: COMPILER=clang++-11
+    - env: COMPILER=clang++-12
 
   fast_finish: true
 
@@ -64,7 +65,7 @@
         # https://apt.llvm.org/
         LLVM_REPO=${COMPILER/clang++/llvm-toolchain-${TRAVIS_DIST}}
         travis_retry wget -nv -O - "https://apt.llvm.org/llvm-snapshot.gpg.key" | sudo apt-key add -
-        travis_retry sudo add-apt-repository -y "deb http://apt.llvm.org/${TRAVIS_DIST}/ ${LLVM_REPO%-11} main"
+        travis_retry sudo add-apt-repository -y "deb http://apt.llvm.org/${TRAVIS_DIST}/ ${LLVM_REPO%-12} main"
         travis_retry sudo apt-get -qq update
         ;;
     esac