meson/win32: There is no need install OpenGL headers on win32

The libraries that use OpenGL already handling the non-exist of OpenGL headers for both
MSVC and MINGW, so there is no need install them

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14019>

include/meson.build

@@ -28,7 +28,7 @@ if with_android_stub
   inc_include += [include_directories('android_stub')]
 endif
 
-if not with_glvnd
+if not with_glvnd and host_machine.system() != 'windows'
   if with_gles1 or with_gles2 or with_opengl or with_egl
     install_headers('KHR/khrplatform.h', subdir : 'KHR')
   endif