mozjs_sys compile error

mozjs_sys compile error.md

   Compiling mozjs_sys v0.0.0 (https://github.com/servo/mozjs#2af5849a)
error: failed to run custom build command for `mozjs_sys v0.0.0 (https://github.com/servo/mozjs#2af5849a)`
Process didn't exit successfully: `V:/3rd-party/servo-clean/target\debug\build\mozjs_sys-661d4efe7c7ca939\build-script-build` (exit code: 101)
--- stdout
touch /v/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/js/src/configure
cd /v/3rd-party/servo-clean/target/debug/build/mozjs_sys-661d4efe7c7ca939/out && \
PYTHON=""c:/python27/python.exe"" \
MOZ_TOOLS="/" CC="gcc" CPP="gcc -E" CXX="g++" AR="ar" \
/v/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/js/src/configure --disable-jemalloc --disable-js-shell --disable-tests --disable-shared-js --without-intl-api --disable-export-js --without-pthreads || (cat config.log && exit 1)
checking for host system type... x86_64-pc-mingw64
checking for target system type... x86_64-pc-mingw64
checking for yasm...
--- stderr
makefile.cargo:65: extraneous text after 'else' directive
Reexecuting in the virtualenv
Traceback (most recent call last):
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/js/src/../../configure.py", line 94, in <module>
    sys.exit(main(sys.argv))
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/js/src/../../configure.py", line 22, in main
    sandbox.run(os.path.join(os.path.dirname(__file__), 'moz.configure'))
  File "V:\3rd-party\servo-clean\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\mozjs\python\mozbuild\mozbuild\configure\__init__.py", line 164, in run
    self.exec_file(path)
  File "V:\3rd-party\servo-clean\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\mozjs\python\mozbuild\mozbuild\configure\__init__.py", line 157, in exec_file
    exec(code, self)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/moz.configure", line 61, in <module>
    include(toolchain_include)
  File "V:\3rd-party\servo-clean\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\mozjs\python\mozbuild\mozbuild\configure\__init__.py", line 344, in include_impl
    self.exec_file(what)
  File "V:\3rd-party\servo-clean\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\mozjs\python\mozbuild\mozbuild\configure\__init__.py", line 157, in exec_file
    exec(code, self)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/build/moz.configure/toolchain.configure", line 9, in <module>
    yasm = check_prog('YASM', ['yasm'], allow_missing=True)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/build/moz.configure/checks.configure", line 63, in check_prog
    @checking('for %s' % var.lower(), lambda x: x or 'not found')
  File "V:\3rd-party\servo-clean\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\mozjs\python\mozbuild\mozbuild\configure\__init__.py", line 327, in decorator
    self._results[func] = func(*resolved_args)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/build/moz.configure/checks.configure", line 34, in wrapped
    ret = func(*args, **kwargs)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/build/moz.configure/checks.configure", line 68, in check
    result = find_program(prog)
  File "V:/3rd-party/servo-clean/.cargo/git/checkouts/mozjs-fa11ffc7d4f1cc2d/master/mozjs/build/moz.configure/util.configure", line 57, in find_program
    from which import which, WhichError
ImportError: No module named which
cat: config.log: No such file or directory
make: *** [makefile.cargo:83: all] Error 1
thread 'main' panicked at 'assertion failed: result.success()', V:/3rd-party/servo-clean/.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\master\build.rs:17
note: Run with `RUST_BACKTRACE=1` for a backtrace.

This was caused by trying to compile the repo on a case-sensitive file system, which is not properly supported by virtualenv: pypa/virtualenv#935