ci: add clang 12 (dev snapshot) to Travis CI build matrix

Change-Id: I45266be56d700434b84aab5f5954828f5df1b598

.jenkins.d/00-deps.sh

@@ -25,7 +25,7 @@ if has OSX $NODE_LABELS; then
 
 elif has Ubuntu $NODE_LABELS; then
     sudo apt-get -qq update
-    sudo apt-get -qy install g++ pkg-config python3-minimal \
+    sudo apt-get -qy install build-essential pkg-config python3-minimal \
                              libboost-all-dev libssl-dev libsqlite3-dev \
                              libpcap-dev
 

.travis.yml

@@ -27,6 +27,7 @@ jobs:
     - env: COMPILER=clang++-8
     - env: COMPILER=clang++-10
     - env: COMPILER=clang++-11
+    - env: COMPILER=clang++-12
 
     # macOS
     - os: osx
@@ -52,7 +53,7 @@ jobs:
     - env: COMPILER=g++-5
     - env: COMPILER=g++-6
     - env: COMPILER=clang++-4.0
-    - env: COMPILER=clang++-11
+    - env: COMPILER=clang++-12
 
   fast_finish: true
 
@@ -69,7 +70,7 @@ before_install:
         # 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