Use the callsite span of a macro expansion in compiletest

[fpoli]

The following test fails, because compiletest does not look for the callsite span of a macro expansion:

macro_rules! macro_with_error {
    ( ) => {
        let x: u64 = true;
    };
}

fn main() {
    macro_with_error!();  //~ ERROR mismatched types
}

This causes some problems when the macro definition is not in the file that is tested, see issue Manishearth/compiletest-rs#48, because there is no way to expect the error with an //~ ERROR comment.

Does the current implementation ignore the callsite of macro expansions on purpose?
If not, I have a fix for this: Manishearth/compiletest-rs#116

[Mark-Simulacrum]

cc @nrc @jseyfried

It might be best to open a PR with the changes if that's relatively trivial to do; I think you'd be more likely to get faster feedback then.

[fpoli]

Fixed in 6a1c063