Sccache didn't take rustc version into hash calculation

[Xuanwo]

    > For example, I ran into issues with `sccache` after upgrading the Rust toolchain. The cached binary object was missing logic present in the latest commit.

Oh, it must be a bug. Scache should generate different cache path after rust toolchain bumped.

sccache/src/compiler/rust.rs

Lines 378 to 383 in 1a82863

	let host = rustc_verbose_version
	.lines()
	.find(|l| l.starts_with("host: "))
	.map(|l| &l[6..])
	.context("rustc verbose version didn't have a line for `host:`")?
	.to_string();

So far we only take host into consideration. I will work on fixing this.

Originally posted by @Xuanwo in #1528 (comment)