Remove the "If only executable code is distributed..." paragraph from
the license text. Everything now uses a normal MIT license.
The only code from Khronos that's included in libglvnd is the EGL/GL
header and XML files, which do not contain that paragraph.
Fixes https://gitlab.freedesktop.org/glvnd/libglvnd/-/issues/221
testglxqueryversion will now call XQueryExtension to check whether the server
supports the GLX extension. If it doesn't, then it will skip the test instead
of reporting it as a failure.
https://github.com/NVIDIA/libglvnd/issues/93
