Another try for Linux Travis

cmake/travis_script_linux.sh

 if [ "$CC" = "gcc" ]; then export CC="gcc-4.8"; fi
 if [ "$CXX" = "g++" ]; then export CXX="g++-4.8"; fi
 
+if [ "$CC" = "clang" ]; then export CC="clang-3.5"; fi
 if [ "$CXX" = "clang++" ]; then export CXX="clang++-3.5"; fi
 
 git clone https://github.com/hpicgs/glbinding.git

src/deps/imgui/imconfig.h

 #define IMGUI_INCLUDE_IMGUI_USER_H
 
 //---- Define implicit cast operators to convert back<>forth from your math types and ImVec2/ImVec4.
-#include <glm/vec2.hpp>
 #define IM_VEC2_CLASS_EXTRA                                                \
         ImVec2(const glm::vec2& f) { x = f.x; y = f.y; }                   \
         operator glm::vec2() const { return glm::vec2(x, y); }
 
-#include <glm/vec4.hpp>
 #define IM_VEC4_CLASS_EXTRA                                                \
         ImVec4(const glm::vec4& f) { x = f.x; y = f.y; z = f.z; w = f.w; } \
         operator glm::vec4() const { return glm::vec4(x,y,z,w); }