lang/rust, lang/rust-nightly: Update to 1.15.1 and 1.17.0 respectively
Both versions of Rust seen changes to their build system. Now they
require a bootstrap of Cargo and thus, a snapshot of Cargo's registry.
Each library has its own suffix instead of a common suffix for a given
version of Rust. Thus all future updates of the ports will include
changes to their plist.
$DISTFILES are now all under the rust directory in $DISTDIR. A
similar change will be committed to devel/cargo later.
lang/rust-nightly is enabled on i386 (bugzilla 216143). The source
snapshot also contains everything to build it on aarch64, but enabling
it will be committed later.
PR: 216143
Approved by: riggs, bapt (mentor), antoine (mentor)
Differential Revision: https://reviews.freebsd.org/D9286