[gtksourceview] build: ignore -Wincompatible-pointer-types-discards-qualifiers on clang

[Christian Hergert <chergert src gnome org>]

commit 0fa231279c7c54768203a69a1bc414b423a1304b
Author: Christian Hergert <chergert redhat com>
Date:   Fri Nov 6 10:34:13 2020 -0800

    build: ignore -Wincompatible-pointer-types-discards-qualifiers on clang
    
    This spews a lot of warnings due to GType registration in GObject. When that
    is fixed we can remove this.

 meson.build | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/meson.build b/meson.build
index c0988c91..ae2bbd09 100644
--- a/meson.build
+++ b/meson.build
@@ -252,6 +252,13 @@ else
     '-Wunused',
     '-fno-strict-aliasing',
   ]
+
+  # Ignore some Werror for clang until GLib fixes volatile usage in
+  # GType registration.
+  if meson.get_compiler('c').get_id() == 'clang'
+    test_c_args += ['-Wno-incompatible-pointer-types-discards-qualifiers']
+  endif
+
   if buildtype != 'plain'
     test_c_args += '-fstack-protector-strong'
   endif