scons: builtin_glsl_function on windows needs bundled getopt.

src/SConscript

@@ -1,9 +1,17 @@
 Import('*')
 
+
 if env['platform'] == 'windows':
     SConscript('getopt/SConscript')
 
 SConscript('glsl/SConscript')
+
+if env['hostonly']:
+    # We are just compiling the things necessary on the host for cross
+    # compilation
+    Return()
+
+
 # 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
 # in mapi/glapi-shared/SConscript.  mesa/SConscript also adapts itself to