[vtk-developers] OSMesa regression

[Bill Lorensen]

The commit at the end of thie email causes my Offscreen build to fail
with errors like these:
[100%] Linking C shared library ../../../lib/libvtkgl2ps-7.1.so
CMakeFiles/vtkgl2ps.dir/gl2ps.c.o: In function `gl2psAddText':
/home/lorensen/ProjectsGIT/VTKGitlab/ThirdParty/gl2ps/vtkgl2ps/gl2ps.c:885:
undefined reference to `glGetBooleanv'
/home/lorensen/ProjectsGIT/VTKGitlab/ThirdParty/gl2ps/vtkgl2ps/gl2ps.c:887:
undefined reference to `glGetFloatv'
/home/lorensen/ProjectsGIT/VTKGitlab/ThirdParty/gl2ps/vtkgl2ps/gl2ps.c:916:
undefined reference to `glGetFloatv'
/home/lorensen/ProjectsGIT/VTKGitlab/ThirdParty/gl2ps/vtkgl2ps/gl2ps.c:936:
undefined reference to `glPassThrough'
...

commit 561c9b6403f4562d91e4fe36e55713747fa22d39
Author: Utkarsh Ayachit <utkarsh.ayachit at kitware.com>
Date:   Wed Jul 6 15:26:57 2016 -0400

    Add support for on and off screen Mesa in same build.

    On and Off scrreen Mesa can now be enabled in the same version of VTK.
    Tested with Mesa 12.0.0-rc2, but has been reported to work with 11.2 as
    well.