The client-side library libNX_GL.{a,so} is not built when building nx-libs.

 However, nx-X11/lib/GL/** ships several imake include files
 (Imakefile.inc) that are also used in nx-X11/programs/Xserver/GL/**.
 These files have been moved from the nx-X11/lib/GL/ code subtree to the
 nx-X11/programs/Xserver/GL/.

 Furthermore, we don't provide module builds of the GL extension anymore,
 as that feature is neither used in nx-libs.