Auto merge of #149273 - bjorn3:crate_locator_improvements, r=petrochenkov

Don't leak sysroot crates through dependencies

Previously if a dependency of the current crate depended on a sysroot crate, then `extern crate` would in the current crate would pick the first loaded version of said sysroot crate even in case of an ambiguity. This is surprising and brittle. For `-Ldependency=` we already blocked this since rust-lang/rust#110229, but the fix didn't account for sysroot crates.

Should fix rust-lang/rust#147966

Author: bors