Rollup merge of #85534 - csmoe:demagnle-assert, r=michaelwoerister
Rollup merge of #85534 - csmoe:demagnle-assert, r=michaelwoerister

add rustc-demangle assertion on mangled symbol

cc https://github.com/rust-lang/rust/issues/60705#issuecomment-844880365
r? `@michaelwoerister`

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