meson: revert glvnd workaround

This effectively reverts MR !2112.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

include/meson.build

@@ -22,7 +22,7 @@ inc_include = include_directories('.')
 inc_d3d9 = include_directories('D3D9')
 inc_haikugl = include_directories('HaikuGL')
 
-if not glvnd_has_headers_and_pc_files
+if not with_glvnd
   if with_gles1 or with_gles2 or with_opengl or with_egl
     install_headers('KHR/khrplatform.h', subdir : 'KHR')
   endif