Rollup merge of #119884 - GuillaumeGomez:rename-env-opt, r=davidtwco

Rename `--env` option flag to `--env-set`

As discussed [on zulip](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Stabilizing.20.60--env.60.20option.20flag.3F). We rename `--env` to not conflicting names with the [RFC](rust-lang/rfcs#2794).

r? `@davidtwco`

Author: GuillaumeGomez