The repository information for cloning the OpenXR repository, rather than just
downloading the source archive, was outdated.
* Use the OpenXR-SDK repository link, not the OpenXR-SDK-Source one. Only the
former is needed, it contains pregenerated files with minimum dependencies.
The latter contains additional tools and the un-generated source files.
* Update the commit hash to the version we currently use, 1.0.14 (was 1.0.6).
Differential Revision: https://developer.blender.org/D10373
Reviewed by: Bastien Montagne
34155dd29b