Add travis build for coverage

Author: yumibagge

.travis.yml

@@ -146,6 +146,36 @@ jobs:
         - EXTRA_CXXFLAGS="-DDEBUG"
       script: echo "Not running any tests for a debug build."
 
+    # Ubuntu Linux with glibc using g++-7, coverage mode
+    - stage: Test different OS/CXX/Flags
+      os: linux
+      sudo: false
+      compiler: gcc
+      cache: ccache
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+            - jq
+            - gdb
+      before_install:
+        - mkdir bin
+        - ln -s /usr/bin/gcc-7 bin/gcc
+        - ln -s /usr/bin/g++-7 bin/g++
+      install:
+        - cmake -H. -Bbuild '-Denable_coverage=1' '-Dparallel_tests=2' '-DCMAKE_CXX_COMPILER=/usr/bin/g++-7'
+        - git submodule update --init --recursive
+        - make -C build coverage
+      env:
+        - COMPILER="ccache /usr/bin/g++-7"
+        - EXTRA_CXXFLAGS="-DDEBUG"
+      script: echo "Running any tests for a debug build."
+      after_success:
+        # codecov
+        - bash <(curl -s https://codecov.io/bash)
+
     # Ubuntu Linux with glibc using clang++-7, debug mode, disable USE_DSTRING
     - stage: Test different OS/CXX/Flags
       os: linux