Fix: Prevent macro-expanded extern crates from shadowing extern arguments
prevents an ICE by fixing a logic bug in `build_reduced_graph.rs`.
the bug caused the compiler to correctly detect and report a shadowing error for a macro-expanded `extern crate` but then continue processing the invalid item, corrupting the resolver's internal state (`extern_prelude`) and leading to a crash in later resolution passes the fix adds an early return after the shadowing error is reported to ensure the invalid item is not added to the resolution graph.
Fixesrust-lang/rust#149821
47f1502c73