rust-bin out of sync, thunderbird fails to build

[Greg Troxel <gdt%lexort.com@localhost>]

lang/rust is at 1.79.0 but lang/rust-bin is at 1.76.0.  I am guessing
this is a mistake as there is lang/rust176-bin.  I think it's important
to keep rust-bin in sync with rust, because people use rust-bin when
they can't cope with builing rust (machines without large RAM, just cpu
cycles, whatever).

With rust-bin 1.76 (N10/amd64), thunderbird is not building.  But,
thunderbird says that it needs 1.41.0, so this seems to be another bug.
It could be related, so I mention it here.