Add test for #48508

This is named for the issue as it's testing the specific details of that
bug. It's a bit tricky as the ICE requires multiple files and debug info
enabled to trigger.

src/test/run-pass/issue-48508-aux.rs

@@ -0,0 +1,16 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-test Not a test. Used by issue-48508.rs
+
+pub fn other() -> f64 {
+    let µ = 1.0;
+    µ
+}

src/test/run-pass/issue-48508.rs

@@ -0,0 +1,27 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for issue #48508:
+//
+// Confusion between global and local file offsets caused incorrect handling of multibyte character
+// spans when compiling multiple files. One visible effect was an ICE generating debug information
+// when a multibyte character is at the end of a scope. The problematic code is actually in
+// issue-48508-aux.rs
+
+// compile-flags:-g
+
+#![feature(non_ascii_idents)]
+
+#[path = "issue-48508-aux.rs"]
+mod other_file;
+
+fn main() {
+    other_file::other();
+}