[patch] Fix use after free in BitcodeReader.cpp error path

[Rafael Espíndola]

> I haven't looked too closely. Is it that bad to make Error() take an
> std::string? Does this leak through the C API or something?

No, this part is fine. The issue is that I want to use this to
implement an IRObjecFile, so I have to expose any errors via a
error_code. This means that the error has to be a simple one (think
type-safe errno) or we have to add a std::string to error_code.

> Nick

Cheers,
Rafael