Rust invocation for Firefox on 32bit Windows is failing

Firefox's configure is failing when checking for a functional rustc with

 0:32.86 DEBUG: Executing: `/var/tmp/dist/rust/bin/rustc --crate-type staticlib --target=i686-pc-windows-gnu -o /tmp/conftest66YTEr.rlib /tmp/conftestkSgS7j.rs`
 0:32.86 DEBUG: The command returned non-zero exit status 101.
 0:32.86 DEBUG: Its error output was:
 0:32.86 DEBUG: | error: the crate `panic_unwind` does not have the panic strategy `unwind`
 0:32.86 DEBUG: |
 0:32.86 DEBUG: | error: aborting due to previous error
 0:32.86 DEBUG: |
 0:32.86 ERROR: Cannot compile for i686-w64-mingw32 with /var/tmp/dist/rust/bin/rustc

Firefox is getting compiled with panic=abort (https://dxr.mozilla.org/mozilla-central/source/testing/geckodriver/.cargo/config) for 32bit Windows and we intend to create a Rustc compiler with that panic strategy as well, given that cross-compiling with panic=unwind is not working (see: comment:1:ticket:25894).

While compiling every crate in the std lib with panic-abort is working it seems we still miss some crucial bit here.

One option to test would be if we can get rid of panic_unwind if we don't need it anyway when compiling for 32bit Windows. For what it is worth, the compiler as we have it right now is working for tor compiled with Rust.