[gtk: 3/4] Fix compilation of c++ test: cpp_args

[Matthias Clasen <matthiasc src gnome org>]

commit 12d591178e53ed8ab9c1568d278f1382f25db6bf
Author: Dan Cîrnaț <dan alt md>
Date:   Tue May 4 13:52:21 2021 +0200

    Fix compilation of c++ test: cpp_args
    
    The correct meson argument for c++ is cpp_args.
    Remove unnecessary(?) "-Idummy-headers" - breaks build

 testsuite/gtk/meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/testsuite/gtk/meson.build b/testsuite/gtk/meson.build
index 42151a5ad3..bf812be140 100644
--- a/testsuite/gtk/meson.build
+++ b/testsuite/gtk/meson.build
@@ -222,7 +222,7 @@ endforeach
 if add_languages('cpp', required: false, native: false)
   test_exe = executable('autotestkeywords',
     sources: 'autotestkeywords.cc',
-    c_args: test_cargs + ['-Idummy-headers'],
+    cpp_args: test_cargs,
     dependencies: libgtk_dep,
     install: get_option('install-tests'),
     install_dir: testexecdir,