Specify the correct C++ libraries for clang in linux OSes.
Activate clang compilation
Remove unused commands.
Revert "Activate clang compilation"

This reverts commit 3240fdeebae798f122dd80f26ce98ffaf9e3a6e5.
For some reason, we have compilation errors with Qt5 in Travis CI but not in my
local machine. Let's disable this for now.
Merge pull request #80 from DO-CV/fix-clang-compilation-in-linux

[MAINT] Specify the correct C++ libraries for clang in linux OSes.