Get ourselves a MIR-full libstd for the host and a foreign architecture
    Updating crates.io index
 Downloading crates ...
  Downloaded hashbrown v0.3.0
  Downloaded rustc-std-workspace-alloc v1.0.0
   Compiling cc v1.0.35
   Compiling core v0.0.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/libcore)
   Compiling libc v0.2.51
   Compiling build_helper v0.1.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/build_helper)
   Compiling unwind v0.0.0 (/home/travis/.rustup/toolchains/master/lib/rustlib/src/rust/src/libunwind)
   Compiling rustc-std-workspace-alloc v1.0.0
error[E0463]: can't find crate for `std`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0463`.