Move GLIB_DISABLE_DEPRECATION_WARNINGS define to a more general place.

build/config/linux/BUILD.gn

Index: build/config/linux/BUILD.gn
diff --git a/build/config/linux/BUILD.gn b/build/config/linux/BUILD.gn
index f26b5101da6cbfc6f48bf7da7c838bde6ae32501..cc7be1ab02df2cf752856a0258fd4eeb79c72a71 100644
--- a/build/config/linux/BUILD.gn
+++ b/build/config/linux/BUILD.gn
@@ -143,7 +143,14 @@ if (use_brlapi) {
 
 pkg_config("gio_config") {
   packages = [ "gio-2.0" ]
-  defines = [ "USE_GIO" ]
+  # glib >=2.40 deprecate g_settings_list_schemas in favor of
+  # g_settings_schema_source_list_schemas. This function is not available on
+  # earlier versions that we still need to support (specifically, 2.32), so
+  # disable the warning with the GLIB_DISABLE_DEPRECATION_WARNINGS define.
+  # TODO(mgiuca): Remove this suppression when we drop support for Ubuntu 13.10
+  # (saucy) and earlier. Update the code to use
+  # g_settings_schema_source_list_schemas instead.
+  defines = [ "USE_GIO", "GLIB_DISABLE_DEPRECATION_WARNINGS" ]
   ignore_libs = true  # Loader generated below.
 }