Travis: Only do a build in the first stage

Tests are run, otherwise using the very same configuration as the primary build,
in the second stage. As all tasks within one stage run in parallel, the ~20mins
that test execution takes will pass while also doing other work rather than
blocking progress to the next stage. Via ccache we will avoid spending time for
re-building.

Author: tautschnig

.travis.yml

@@ -4,7 +4,7 @@ jobs:
   include:
 
     - &formatting-stage
-      stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 test
+      stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 build
       env: NAME="clang-format"
       addons:
         apt:
@@ -32,13 +32,13 @@ jobs:
       before_cache:
 
     - &linter-stage
-      stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 test
+      stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 build
       env: NAME="CPP-LINT"
       install:
       script: scripts/travis_lint.sh
       before_cache:
 
-    - stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 test
+    - stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 build
       env: NAME="DOXYGEN-CHECK"
       addons:
         apt:
@@ -62,7 +62,30 @@ jobs:
         - scripts/publish_doc.sh
 
     # Ubuntu Linux with glibc using g++-5
-    - stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 test
+    - stage: Linter + Doxygen + non-debug Ubuntu/gcc-5 build
+      os: linux
+      sudo: false
+      compiler: gcc
+      cache: ccache
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - libwww-perl
+            - g++-5
+            - libubsan0
+            - parallel
+      before_install:
+        - mkdir bin ; ln -s /usr/bin/gcc-5 bin/gcc
+      # env: COMPILER=g++-5 SAN_FLAGS="-fsanitize=undefined -fno-sanitize-recover -fno-omit-frame-pointer"
+      env:
+        - COMPILER="ccache /usr/bin/g++-5"
+        - EXTRA_CXXFLAGS="-D_GLIBCXX_DEBUG"
+      script: echo "Test are run in the next stage."
+
+    # Ubuntu Linux with glibc using g++-5
+    - stage: Test different OS/CXX/Flags
       os: linux
       sudo: false
       compiler: gcc