Address LLVM assertion failure by prepopulating with *just* name-anon-globals.

Author: pnkfelix

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

@@ -20,7 +20,7 @@
 // aux-build:lib.rs
 
 // rust-lang/rust#56772: nikic says we need this to be proper test.
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -C no-prepopulate-passes -C passes=name-anon-globals
 
 extern crate lib;