Dead functions in middle::trans::shape can't be removed

[catamorphism]

If I remove the functions add_u16 and add_substr, which are never called, from middle::trans::shape, I get:

/Users/tchevalier/rust/src/libstd/std.rc:28:0: 28:30 error: can't find crate for `core`
/Users/tchevalier/rust/src/libstd/std.rc:28 extern mod core(vers = "0.4");
                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

when building stage1 libstd. @pcwalton says this is due to a problem with LLVM metadata getting truncated.

If so, we should isolate this to the piece of LLVM bytecode that exhibits the problem, and report it upstream.

[lucab]

I've experienced the exact same issue when building 0.4-incoming using Debian packaged llvm-3.1. On that same system, building 0.3.1 with external llvm works, as well as using llvm submodule for 0.4.