Change cygwin to use C locale - std::ctype yields incorrect results for xdigit class on this platform.

[SVN r64628]

libs/regex

@@ -1 +1 @@
-Subproject commit 2b2fbdb02674a911d004bf7555d7f23b5edaaf6a
+Subproject commit 6d53e5ecae61464635903d215f25abafc3062238