security/gnupg: Use gpgrt-config for configure

Use gpgrt-config in the configure stage over the old individual
*-config scripts from the various gnupg-related libraries (e.g:
gpg-error-config, libassuan-config, ksba-config). Upstream has
prefered this method since version 2.3.0 released 2021-04-07 and
the old scripts are now starting to be phased-out.

This prepares for devel/npth >= 1.7 which no longer installs
npth-config by default, so gpgrt-config must be used to get its
configuration details.

Approved by:	portmgr (blanket)

security/gnupg/files/patch-configure

+Fix path of pkgconfig files passed to gpgrt-config.
+
+--- configure.orig	2024-01-25 10:09:44 UTC
++++ configure
+@@ -8428,7 +8428,7 @@ fi
+     # Get the prefix of gpgrt-config assuming it's something like:
+     #   <PREFIX>/bin/gpgrt-config
+     gpgrt_prefix=${GPGRT_CONFIG%/*/*}
+-    possible_libdir1=${gpgrt_prefix}/lib
++    possible_libdir1=${gpgrt_prefix}/libdata
+     # Determine by using system libdir-format with CC, it's like:
+     #   Normal style: /usr/lib
+     #   GNU cross style: /usr/<triplet>/lib