Remove extra build with NDEBUG that compiles but doesn't test.

Instead, add NDEBUG to a linux clang build that runs regression.

Author: andreast271

.travis.yml

@@ -115,7 +115,7 @@ jobs:
         - EXTRA_CXXFLAGS="-DDEBUG"
       script: echo "Not running any tests for a debug build."
 
-    # Ubuntu Linux with glibc using clang++-3.7
+    # Ubuntu Linux with glibc using clang++-3.7, no-debug mode
     - stage: Test different OS/CXX/Flags
       os: linux
       sudo: false
@@ -138,6 +138,7 @@ jobs:
       env:
         - COMPILER="ccache clang++-3.7 -Qunused-arguments -fcolor-diagnostics"
         - CCACHE_CPP2=yes
+        - EXTRA_CXXFLAGS="-DNDEBUG"
 
     # Ubuntu Linux with glibc using clang++-3.7, debug mode
     - stage: Test different OS/CXX/Flags
@@ -165,32 +166,6 @@ jobs:
         - EXTRA_CXXFLAGS="-DDEBUG"
       script: echo "Not running any tests for a debug build."
 
-    # Ubuntu Linux with glibc using clang++-3.7, no-debug mode
-    - stage: Test different OS/CXX/Flags
-      os: linux
-      sudo: false
-      compiler: clang
-      cache: ccache
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-3.7
-          packages:
-            - libwww-perl
-            - clang-3.7
-            - libstdc++-5-dev
-            - libubsan0
-      before_install:
-        - mkdir bin ; ln -s /usr/bin/clang-3.7 bin/gcc
-        - export CCACHE_CPP2=yes
-      env:
-        - COMPILER="ccache clang++-3.7 -Qunused-arguments -fcolor-diagnostics"
-        - CCACHE_CPP2=yes
-        # Disable known warnings caused by -DCPROVER_INVARIANT_DO_NOT_CHECK.
-        - EXTRA_CXXFLAGS="-DNDEBUG -DCPROVER_INVARIANT_DO_NOT_CHECK -Wno-return-type -Wno-unused-variable -Wno-sometimes-uninitialized -Wno-unused-function"
-      script: echo "Not running any tests for a debug build."
-
     # cmake build using g++-5
     - stage: Test different OS/CXX/Flags
       os: linux