Include pretty printers for libc++ when Python is enabled.

The pretty printers are pulled from github/bsdjhb/libcxx-gdbpy.git.
They are not complete and only support a subset of STL classes.

Bump PORTREVISION.

PR: 235539
Reviewed by: pizzamig (maintainer)
Differential Revision: https://reviews.freebsd.org/D19087