build: Add missing argument to add_languages()

We need to specify whether we want a native compiler or not.

testsuite/gtk/meson.build

@@ -112,7 +112,7 @@ foreach t : tests
 endforeach
 
 # FIXME: if objc autotestkeywords_CPPFLAGS += -DHAVE_OBJC=1 -x objective-c++
-if add_languages('cpp', required: false)
+if add_languages('cpp', required: false, native: false)
   test_exe = executable('autotestkeywords',
                         'autotestkeywords.cc',
                         c_args : test_cargs + ['-Idummy-headers'],