* [xerces-c] Update REF and SHA512
* [sfml] re-trigger ci
* [pcl] re-trigger ci
* [boost-signals] re-trigger ci
* [tmxparser] re-trigger ci
* [soil2] switch repo to github
* [gtest] re-trigger ci
Cmake doesn't find opengl on Ubuntu (tried 18.04, 19.04) even after installing the required system dependencies.
libgl1-mesa-dev works instead of mesa-common-dev, as noted here: https://stackoverflow.com/a/47926071/6597851.
Just replacing export symbols doesn't really do the trick as the config file still won't find the static libraries, by "forcing" the `SFML_STATIC_LIBRARIES` to true when using the static target, the SFMLConfig.cmake and SFMLConfigDependencies.cmake files will properly detect the static libraries and it will also set the config header correctly.
