Log message:
Pullup ticket #6432 - requested by mlelstv
www/squid4: build fix

(via patch)

building squid4 requires 64bit atomics. In pkgsrc-HEAD there is
mk/atomics64.mk with the necessary dependencies and www/squid4 includes
it.

In release 2020Q4 this is missing, so a simple pullup of the package
isn't sufficient unless mk/atomics64.mk is also pulled up.