glib: Update various code comments to mention Meson

Rather than referring to the old autotools build system.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

gio/tests/gschema-compile.c

@@ -11,11 +11,6 @@ typedef struct {
   const gchar *err;
 } SchemaTest;
 
-/* Meson build defines this, autotools build does not */
-#ifndef GLIB_COMPILE_SCHEMAS
-#define GLIB_COMPILE_SCHEMAS "../glib-compile-schemas"
-#endif
-
 static void
 test_schema_do_compile (gpointer data)
 {
@@ -23,7 +18,7 @@ test_schema_do_compile (gpointer data)
   gchar *filename = g_strconcat (test->name, ".gschema.xml", NULL);
   gchar *path = g_test_build_filename (G_TEST_DIST, "schema-tests", filename, NULL);
   const gchar *argv[] = {
-    GLIB_COMPILE_SCHEMAS,
+    GLIB_COMPILE_SCHEMAS,  /* defined in meson.build */
     "--strict",
     "--dry-run",
     "--schema-file", path,