Crash when isnan is called from two different source files

[sampsyo]

Here's a truly strange bug: compiling this application crashes, even with optimizations disabled (make build_orig). https://github.com/uwsampa/accept-apps/tree/master/test

Just calling isnan() from two different files is enough to crash. This doesn't happen if the code is combined in one file. I suspect a bug in llvm-link.