Add option to explicitly disable ICU support.

Update docs to describe new ICU config support.

[SVN r65489]

libs/regex

@@ -1 +1 @@
-Subproject commit 6c24ae271803b6213a20b37159c1f85b525cc60d
+Subproject commit 383f3b21441dd7f8211b6beefd8047d876ec2562