Travis always has massive backlog of macOS builds, so we can't rely on them
too much.
The iphone build was mostly useful to spot tools=no or target=release_debug
issues, so replacing it by an appropriate X11 build.
Now that AppVeyor handles testing Windows builds with MSVC,
we can skip the need to test against Travis' old MinGW toolchain
and have a faster CI process.
Also try building X11 binaries against system OpenSSL, should
speed up build.
Commits or PRs that do not respect the clang-format style that we
enforce will fail the test.
Adding ubuntu-toolchain-r-test as its libstdc++ is necessary to install
libllvm-3.9.
As we say in French, "Trop, c'est trop !".
Those builds fail 50% of the time due to timeouts, it's pointless to have them until we
find a better solution to install the Android SDK and NDK.
Workaround for #6973.
Builds tend to fail due to the 10 min limit for stalled builds.
Most likely because the download is done silently and takes more than
10 min depending on the Travis connection.
Now it test 6 builds:
* Ubuntu 14.04 - x11 (g++)
* Ubuntu 14.04 - x11 (clang++)
* Ubuntu 14.04 - windows (via MinGW)
* OS X - osx (g++)
* OS X - osx (clang++)
* OS X - android
* OS X - iphone
Instead of just g++ on Ubuntu 12.04...
