* travis: Enable building qt for linux.
* qb: Set QT_SELECT for moc and qtchooser.
This should have no effect on systems where qtchooser is not used.
Fixes https://github.com/libretro/RetroArch/issues/8028
* qb: Actually disable c++ features if there is no c++ compiler.
Now this warning actually does something.
Warning: A working C++ compiler was not found, C++ features will be disabled.
@twinaphex reported that he was getting a lot of Travis email notifications. These are not needed, as the build status is reported on both Pull Requests, and the Status Badge.
Builds on Linux with gcc and clang, and also on Mac.
Had to configure a more recent version of clang as the default Travis CI
one is a bit outdated and wouldn't work.
Unfortunately I was unable to install Nvidia Cg for Mac as it needs to
run the installer interactively. Still, it builds without Cg support.
It only covers a subset of the architectures, but that's better than
nothing and should catch at least basic errors on pull requests
(requires enabling Travis CI support in the GitHub repository settings).
