dep_glx utilities (x11 ones like glxinfo) get disabled by default when mesa is built without glvnd

the meson.build does:

dep_glx = dependency('glx', required: false, disabler : true)
if not dep_glx.found() and host_machine.system() == 'darwin'
  # xquartz doesn't have a glx.pc, but it does have the header. And all the
  # symbols reside in libGL, so let's just use that.
  if cc.check_header('GL/glx.h', dependencies: dep_x11)
    dep_glx = dep_gl
  endif
endif

essentially, this means "find a glx.pc or disable everything depending on this". that makes sense, however, when using mesa *without* glvnd, it does not install a glx.pc file- even though it installs all the others (gl, egl, ..). see e.g. this and this.

if the darwin workaround removes and host_machine..., the cc.check_header also finds glx via the workaround on a system without glvnd too. see for instance my workaround.

however, i'm not sure if the solution here is to delete that so the workaround works, or to make mesa also install glx.pc when configured without glvnd?