shells/rc: Update to 1.7.4, Fix build

After ports r440197, there is a build problem with the default option.

- Update to 1.7.4 and fix build
- Move MASTER_SITES to the currently upstream address
- Improve pkg-descr
- Set LICENSE

PR:	219596
Approved by:	garga (mentor), maintainer (timeout)
Differential Revision:	https://reviews.freebsd.org/D11126

$ portlint -C
looks fine.