auto merge of #10527 : eholk/rust/win64, r=alexcrichton

This was needed to access UEFI boot services in my new Boot2Rust experiment.

I also realized that Rust functions declared as extern always use the C calling convention regardless of how they were declared, so this pull request fixes that as well.

diff --cc src/librustc/middle/trans/foreign.rs
Simple merge

diff --cc src/libsyntax/abi.rs
Simple merge