lang/rust: Update to 1.55.0

- Set codegen-units=1 [1]
- Add hack to skip cargo update on git sources as a step towards solving [2]
- Fix 'capacity overflow' panics on armv* [3]

Changes:	https://blog.rust-lang.org/2021-09-09/Rust-1.55.0.html
PR:		258337
PR:		256099 [1]
PR:		256581 [2]
PR:		257419 [3]
Reviewed by:	mikael, pkubaj
Exp-run by:	antoine
Differential Revision:	https://reviews.freebsd.org/D31872
With hat:	rust