util/StringUtil: add FindStringSuffix()

src/util/StringUtil.hxx

@@ -90,6 +90,14 @@ gcc_pure
 bool
 StringEndsWith(const char *haystack, const char *needle);
 
+/**
+ * Check if the given string ends with the specified suffix.  If yes,
+ * returns the position of the suffix, and nullptr otherwise.
+ */
+gcc_pure
+const char *
+FindStringSuffix(const char *p, const char *suffix);
+
 /**
  * Copy a string.  If the buffer is too small, then the string is
  * truncated.  This is a safer version of strncpy().