meson: fix private libs when building without glx

I noticed that the generated pkg-config files will include
glx and x11 dependencies even when x11 isn't a selected platform.

This fixes the private libs and was tested by building kmscube

V2:
  - check if gallium-xlib is being used for glx

Fixes: 108d257a16 "meson: build libEGL"
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

meson.build

@@ -1371,18 +1371,24 @@ endforeach
 
 inc_include = include_directories('include')
 
-gl_priv_reqs = [
+gl_priv_reqs = []
+
+if with_glx == 'xlib' or with_glx == 'gallium-xlib'
+  gl_priv_reqs += ['x11', 'xext', 'xcb']
+elif with_glx == 'dri'
+  gl_priv_reqs += [
     'x11', 'xext', 'xdamage >= 1.1', 'xfixes', 'x11-xcb', 'xcb',
     'xcb-glx >= 1.8.1']
+  if with_dri_platform == 'drm'
+    gl_priv_reqs += 'xcb-dri2 >= 1.8'
+  endif
+endif
 if dep_libdrm.found()
   gl_priv_reqs += 'libdrm >= 2.4.75'
 endif
 if dep_xxf86vm.found()
   gl_priv_reqs += 'xxf86vm'
 endif
-if with_dri_platform == 'drm'
-  gl_priv_reqs += 'xcb-dri2 >= 1.8'
-endif
 
 gl_priv_libs = []
 if dep_thread.found()