mu-regex: make backward-compatible with older glib

lib/utils/mu-regex.hh

@@ -28,6 +28,10 @@ namespace Mu {
  * PCRE rather than std::regex because it is much faster.
  */
 struct Regex {
+#if !GLIB_CHECK_VERSION(2,74,0) /* backward compat */
+#define G_REGEX_DEFAULT	      (static_cast<GRegexCompileFlags>(0))
+#define G_REGEX_MATCH_DEFAULT (static_cast<GRegexMatchFlags>(0))
+#endif
 	/**
 	 * Trivial constructor
 	 *
@@ -35,7 +39,6 @@ struct Regex {
 	 */
 	Regex() noexcept: rx_{}  {}
 
-
 	/**
 	 * Construct a new Regex object
 	 *