dev-python/smmap2: A sliding window memory map manager

dev-python/smmap2: A sliding window memory map manager

Smmap wraps an interface around mmap and tracks the mapped files as
well as the amount of clients who use it. If the system runs out of
resources, or if a memory limit is reached, it will automatically
unload unused maps to allow continued operation.

Required to bump dev-python/gitdb (now renamed to gitdb2).

Bug: https://bugs.gentoo.org/619508
Closes: https://github.com/gentoo/gentoo/pull/4740
Package-Manager: Portage-2.3.5, Repoman-2.3.1