Add clang compilation to travis configuration

Swig 2.0.12 is now installed to avoid the use of
Wno-unused-but-set-variable flag which is not present in Clang.
Swig sources are built from the official github release.
Nevertheless Swig installation success is not checked as the
yodl2man command, used for manual generation is not available in
travis whitelist.

Signed-off-by: Jules Clero <julesx.clero@intel.com>

Author: clero

.travis.yml

@@ -8,8 +8,7 @@ env:
 
 compiler:
     - gcc
-    # clang not supported yet
-    # - clang
+    - clang
 
 # Install a recent gcc and gcov,
 # it will not be necessary once travis worker is based on ubuntu > 12.04.
@@ -20,14 +19,21 @@ addons:
         sources:
             - ubuntu-toolchain-r-test
         packages:
-            - swig
             - valgrind
             - g++-4.8
 
 install:
     - pip install --user cpp-coveralls; export PATH=$HOME/.local/bin:$PATH
     - wget --directory-prefix $PREFIX/include
               https://raw.github.com/philsquared/Catch/master/single_include/catch.hpp
+    # Install recent swig.
+    # Avoid make install check because documentation generation will fail as yodl2man command is
+    # missing and the corresponding paquet is not available in travis whitelist.
+    - ( mkdir build_swig && cd build_swig &&
+          wget https://github.com/swig/swig/archive/rel-2.0.12.tar.gz &&
+          tar -xf rel-2.0.12.tar.gz && cd swig-rel-2.0.12/ && ./autogen.sh &&
+          ./configure --prefix=$PREFIX && make && make install ;
+          echo "Dropping documentation generation error" )
 
 before_script:
     - if [ "$CC" = "gcc" ]; then export CC=gcc-4.8 CXX=g++-4.8; fi
@@ -55,6 +61,7 @@ after_success:
           --exclude "build_debug/bindings/python"
           --exclude "build_debug/CMakeFiles"
           --exclude "build"
+          --exclude "build_swig"
           --exclude "skeleton-subsystem"
           --exclude "test/test-subsystem"
           --exclude "bindings/c/Test.cpp"