Revert "Disable "Linux clang-3.9 + coverage" builds which are failing with "The job exceeded the maximum log length, and has been terminated.""

This reverts commit ac19076f0b.

.travis.yml

@@ -43,6 +43,21 @@ matrix:
         apt:
           sources: [ 'ubuntu-toolchain-r-test' ]
           packages: [ 'clang-3.9', 'libstdc++-4.9-dev', 'xutils-dev', 'postgresql-9.5-postgis-2.3' ]
+    - os: linux
+      name: Linux clang-3.9 + coverage
+      env: >-
+          CXX="ccache clang++-3.9 -Qunused-arguments"
+          CC="clang-3.9"
+          COVERAGE=true
+          QUIET=true
+      before_install:
+        - export LINKFLAGS="-fuse-ld=gold-2.26"
+        - export LLVM_COV="llvm-cov-3.9"
+      addons:
+        postgresql: "9.5"
+        apt:
+          sources: [ 'ubuntu-toolchain-r-test' ]
+          packages: [ 'clang-3.9', 'llvm-3.9', 'libstdc++-4.9-dev', 'xutils-dev', 'postgresql-9.5-postgis-2.3' ]
     - os: osx
       name: OSX clang
       # https://docs.travis-ci.com/user/languages/objective-c/#Supported-OS-X-iOS-SDK-versions