meson: Support building without Gst debug

meson.build

@@ -154,6 +154,30 @@ ugly_args = ['-DHAVE_CONFIG_H']
 configinc = include_directories('.')
 libsinc = include_directories('gst-libs')
 
+if gst_dep.type_name() == 'internal'
+    gst_proj = subproject('gstreamer')
+
+    if gst_proj.get_variable('disable_gst_debug')
+        message('GStreamer debug system is disabled')
+        add_project_arguments('-Wno-unused', language: 'c')
+    else
+        message('GStreamer debug system is enabled')
+    endif
+else
+    # We can't check that in the case of subprojects as we won't
+    # be able to build against an internal dependency (which is not built yet)
+    if not cc.compiles('''
+#include <gst/gstconfig.h>
+#ifdef GST_DISABLE_GST_DEBUG
+#error "debugging disabled, make compiler fail"
+#endif''' , dependencies: gst_dep)
+        message('GStreamer debug system is disabled')
+        add_global_arguments('-Wno-unused', language: 'c')
+    else
+        message('GStreamer debug system is enabled')
+    endif
+endif
+
 subdir('gst')
 subdir('ext')
 subdir('tests')