Rollup merge of #44203 - cuviper:compiler-rt-test, r=Mark-Simulacrum
Rollup merge of #44203 - cuviper:compiler-rt-test, r=Mark-Simulacrum

rustbuild: update the rust-src filter for compiler-rt

We wanted `src/compiler-rt/test` filtered from the `rust-src` package,
but that path is now `src/libcompiler_builtins/compiler-rt/test`.  This
saves over half of the installed rust-src size. (50MB -> 22MB)

GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust