travis: hopefully fix use of gcc-4.9

.travis.yml

@@ -22,7 +22,7 @@ matrix:
     # Linux GCC-4.9 release static
     - compiler: gcc-4.9
       addons: *gcc49-packages
-      env: CC=/usr/bin/gcc-4.9 CXX=/usr/bin/g++-4.9 TRAVIS_BUILD_TYPE=Release TRAVIS_SHARED_LIBS=OFF TRAVIS_STRICT_C90=OFF TRAVIS_MAKE_CHECK=ON  TRAVIS_COVERALLS=OFF
+      env: TRAVIS_BUILD_TYPE=Release TRAVIS_SHARED_LIBS=OFF TRAVIS_STRICT_C90=OFF TRAVIS_MAKE_CHECK=ON  TRAVIS_COVERALLS=OFF TRAVIS_GCC_VERSION=4.9
     # OSX Clang debug static
     - os: osx
       compiler: clang

travis-build-script.sh

@@ -18,6 +18,12 @@ echo TRAVIS_COVERALLS=$TRAVIS_COVERALLS
 # CMake
 mkdir build && cd build
 cmake --version
+
+if [ -n "${TRAVIS_GCC_VERSION}" ]; then
+    export CC=gcc-4.9;
+    export CXX=g++-4.9;
+fi
+
 cmake .. -G "Unix Makefiles"       \
          -DCMAKE_DEBUG_POSTFIX=_d  \
          -DCMAKE_BUILD_TYPE=$TRAVIS_BUILD_TYPE \