cmake failure

--- stdout
detected home dir change, cleaning out entire build directory

--- stderr
thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 145, message: "Le r\u{e9}pertoire n\u{201
9}est pas vide." } }', ../src/libcore\result.rs:746
stack backtrace:
   0:   0xb7f78a - std::rt::lang_start::h5b0863080165c75e
   1:   0xb66ad3 - std::sys_common::unwind::begin_unwind_inner::h39d40f52add53ef7
   2:   0xb68140 - std::sys_common::unwind::begin_unwind_fmt::h64c0ff793199cc1b
   3:   0xb76132 - rust_begin_unwind
   4:   0xb3819d - unwrap
                at c:\Users\lqd\Dropbox\code\src\libcore\result.rs:687
   5:   0xb2d236 - maybe_clear
                at C:\Users\lqd\.cargo\registry\src\github.com-48ad6e4054423464\cmake-0.1.17\src\lib.rs:426
   6:   0xb24b5c - build
                at C:\Users\lqd\.cargo\registry\src\github.com-48ad6e4054423464\cmake-0.1.17\src\lib.rs:223
   7:   0xb22aec - build<&str>
                at C:\Users\lqd\.cargo\registry\src\github.com-48ad6e4054423464\cmake-0.1.17\src\lib.rs:89
   8:   0xb211fa - main
                at c:\Users\lqd\Dropbox\code\mir2wasm\build.rs:11
   9:   0xb7f0ed - std::rt::lang_start::h5b0863080165c75e
  10:   0xb7eeb2 - std::rt::lang_start::h5b0863080165c75e
  11:   0xb23be0 - main
  12: 0x76623389 - BaseThreadInitThunk
  13: 0x77689901 - RtlInitializeExceptionChain

This makes cargo+build.rs fail with just this error message:
error: build script output was not valid utf-8