Transmute restrictions are placed on functions called 'transmute'

[brson]

The transmute intrinsic has some special restrictions. The check that implements these does not actually check that the function is a lang item, just looking at the name 'transmute':

extern { fn transmute(); }

fn main() { transmute() }

/home/brian/transmute.rs:5:13: 5:22 error: internal compiler error: transmute wasn't a bare fn?!
/home/brian/transmute.rs:5 fn main() { transmute() }
                                       ^~~~~~~~~
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libsyntax/diagnostic.rs:107

For defs in the local crate it appears this only happens with foreign functions called 'transmute'. From looking at the code, it looks like the cross-crate case isn't so restricted and will try to check every function called 'transmute'.

[huonw]

(I guess this would be an easy fix after #12634.)