Fix gcc warnings from ICU wrappers.

Add optional support for marked sub-expression location information.
Add support for ${n} in format replacement text.
Fixes #2556.
Fixes #2269.
Fixes #2514.

[SVN r50370]

libs/regex

@@ -1 +1 @@
-Subproject commit c997a1fcc692f22b4e8228c17bf6442c50dc2cd4
+Subproject commit b4152cd74d60046c358226719a7f0cad232f7499