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