When using mesa with libglvnd support, mesa will no longer install the gl, glx, egl pkg-config files but instead let libglvnd provide them. libglvnd maintainers decided to change the versioning as it was mesa-specific previously. Now the libraries have versions of the API they expose[1]. This causes problems when building the X server:
checking for glproto >= 1.4.17 gl >= 9.2.0... no configure: error: Package requirements (glproto >= 1.4.17 gl >= 9.2.0) were not met:
Requested 'gl >= 9.2.0' but version of gl is 1.2
Lower the version requirement to 1.2 to allow building against libglvnd provided libraries
[1] https://github.com/NVIDIA/libglvnd/commit/0dfaea2bcb7cdcc785f95e244223bd004a2d7fba