MAINTAINERS: clarify policy with config/ (and other top level files)

MAINTAINERS: clarify policy with config/ (and other top level files)

Rather than copy & paste more text, just merge the existing config/
section with the existing intl/ section.  This ends up clarifying
the policy with that subdir (and top level files) that any commit
made to gcc's repo is allowed to be merged with the sourceware tree
without pre-approval.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>