Can't build 32-bit output on 64-bit Windows

Hey everyone,

I'm struggling to build a Windows 32-bit crate on a 64-bit system. The i686-pc-windows-msvc target is installed, as is the stable-i686-pc-windows-msvc toolchain. If I run cargo +stable-i686-pc-windows-msvc -vvv build --target i686-pc-windows-msvc I get, after lots of output:

     Running `Z:\Projects\tolk\tolk-sys\target\debug\build\tolk-sys-13a758780aa903e9\build-script-build`
[tolk-sys 0.2.0] Error: Os { code: 3, kind: NotFound, message: "The system cannot find the path specified." }
error: failed to run custom build command for `tolk-sys v0.2.0 (Z:\Projects\tolk\tolk-sys)`
Caused by:
  process didn't exit successfully: `Z:\Projects\tolk\tolk-sys\target\debug\build\tolk-sys-13a758780aa903e9\build-script-build` (exit code: 1)
--- stderr
Error: Os { code: 3, kind: NotFound, message: "The system cannot find the path specified." }

Here's what Linux file has to say about the build script:

target/debug/build/tolk-sys-13a758780aa903e9/build-script-build.exe: PE32 executable (console) Intel 80386, for MS Windows

So it seems to exist, but Cargo isn't running or finding it for some reason.

I'm also getting similar issues in Appveyor, which is what revealed this problem to me. The Appveyor environment only installs the I686 Rust toolchain, so I think that rules out accidental leakage of x86-64. I also run the 32-bit Visual Studio setup script. The logs seem to confirm that I'm 32-bit all the way down.

Any help would be greatly appreciated--I've spent a long time looking into this and don't know how to debug it further. For reference, here is the crate I'm attempting to build for 32-bit. Here is my Appveyor script, and a list of logs for the most recent build jobs for comparison.

Thanks for any assistance.