www/nginx-devel: choose PCRE library for build

NGINX 1.21.5 adds support for PCRE2 library, in addition to
support PCRE1. It's possible to choose regular expression
library for the port now.

Please note: several modules are required patching to support
PCRE2 library, so let's keep PCRE1 as default version for now.

Bump PORTREVISION.