scons: Don't build loader on Windows.

EGL was the last user.

Reviewed-by: Brian Paul <brianp@vmware.com>
diff --git a/src/SConscript b/src/SConscript
index 40b7fc1..b0578e8 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -12,7 +12,8 @@
     # compilation
     Return()
 
-SConscript('loader/SConscript')
+if env['platform'] != 'windows':
+    SConscript('loader/SConscript')
 
 # When env['gles'] is set, the targets defined in mapi/glapi/SConscript are not
 # used.  libgl-xlib and libgl-gdi adapt themselves to use the targets defined