Rollup merge of rust-lang#56772 - pnkfelix:issue-54153-linkage-sometimes-requires-optimizations, r=nikic

fix issue 54153 by not testing issue-18804 on Windows nor OS X.

Fix rust-lang#54153

Author: pietroalbini

src/test/run-pass/issues/issue-18804/main.rs

@@ -14,9 +14,14 @@
 
 // ignore-asmjs no weak symbol support
 // ignore-emscripten no weak symbol support
+// ignore-windows no extern_weak linkage
+// ignore-macos no extern_weak linkage
 
 // aux-build:lib.rs
 
+// rust-lang/rust#56772: nikic says we need this to be proper test.
+// compile-flags: -C no-prepopulate-passes -C passes=name-anon-globals
+
 extern crate lib;
 
 fn main() {