Add CI compilation with clang++-3.8

This is to check that changes do not break compilation using
clang++-3.8, as happened with
#4699

Author: romainbrenguier

.travis.yml

@@ -182,6 +182,35 @@ jobs:
         - WITH_MEMORY_ANALYZER=1
       script: echo "Not running any tests for a debug build."
 
+    # Ubuntu Linux with glibc using clang++-3.8, debug mode
+    - stage: Test different OS/CXX/Flags
+      os: linux
+      sudo: false
+      compiler: clang-3.8
+      cache: ccache
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+            - llvm-toolchain-trusty-7
+          packages:
+            - libwww-perl
+            - clang-3.8
+            - libstdc++-5-dev
+            - libubsan0
+            - jq
+            - gdb
+      before_install:
+        - mkdir bin
+        - export CCACHE_CPP2=yes
+      # env: COMPILER=clang++-3.8 SAN_FLAGS="-fsanitize=undefined -fno-sanitize-recover=undefined,integer -fno-omit-frame-pointer"
+      env:
+        - COMPILER="ccache /usr/bin/clang++-3.8"
+        - EXTRA_CXXFLAGS="-Qunused-arguments -fcolor-diagnostics -DDEBUG -DUSE_STD_STRING"
+        - CCACHE_CPP2=yes
+        - WITH_MEMORY_ANALYZER=1
+      script: echo "Not running any tests for a debug build."
+
     # cmake build using g++-7, enable NAMED_SUB_IS_FORWARD_LIST
     - stage: Test different OS/CXX/Flags
       os: linux