Auto merge of #32206 - alexcrichton:fix-windows-rustbuild, r=brson

Fix Windows rustbuild

These commits fix the rustbuild Windows bots, namely:

* The 32-bit build of LLVM was failing because libraries weren't being linked. This was in turn caused by the build script for `rustc_llvm` erroneously detecting that it was cross compiling when it actually wasn't.
* Tools of the build were compiled against the wrong libraries, so running them would fail on Windows as rpath didn't exist and `PATH` was wrong.
* Some linkchecker fixes for Windows paths had to be applied as well.