test_libpng failing occasionally on windows

[sbc100]

This is a very odd one. It must be some kind of race condition, but I can't figure out that would be possible:

https://logs.chromium.org/logs/emscripten-releases/buildbucket/cr-buildbucket/8813262227461617793/+/u/Emscripten_testsuite__other_/stdout

use native object (non-LTO)
cache:INFO:  - ok
cache:INFO: generating port: sysroot\lib\wasm32-emscripten\libpng.a... (this will be cached in "C:\b\s\w\ir\x\w\install\emscripten\cache\sysroot\lib\wasm32-emscripten\libpng.a" for subsequent builds)
root:INFO: building port: libpng
Traceback (most recent call last):
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 4033, in <module>
    sys.exit(main(sys.argv))
  File "C:\b\s\w\ir\cipd_bin_packages\cpython3\bin\Lib\contextlib.py", line 75, in inner
    return func(*args, **kwds)
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 4026, in main
    ret = run(args)
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 1136, in run
    linker_inputs = phase_compile_inputs(options, state, newargs, input_files)
  File "C:\b\s\w\ir\cipd_bin_packages\cpython3\bin\Lib\contextlib.py", line 75, in inner
    return func(*args, **kwds)
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 2718, in phase_compile_inputs
    compile_source_file(i, input_file)
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 2698, in compile_source_file
    cmd = get_clang_command(input_file)
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 2639, in get_clang_command
    return get_compiler(src_file) + get_cflags(state.orig_args) + compile_args + [src_file]
  File "C:\b\s\w\ir\x\w\install\emscripten\\emcc.py", line 888, in get_cflags
    ports.add_cflags(cflags, settings)
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\ports\__init__.py", line 364, in add_cflags
    port.get(Ports, settings, shared)
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\ports\libpng.py", line 47, in get
    return [shared.Cache.get_lib(get_lib_name(settings), create, what='port')]
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\cache.py", line 139, in get_lib
    return self.get(name, *args, **kwargs)
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\cache.py", line 167, in get
    creator(cachename)
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\ports\libpng.py", line 39, in create
    ports.install_headers(dest_path)
  File "C:\b\s\w\ir\x\w\install\emscripten\tools\ports\__init__.py", line 95, in install_headers
    shutil.copyfile(f, os.path.join(dest, os.path.basename(f)))
  File "C:\b\s\w\ir\cache\vpython\33307a\lib\shutil.py", line 264, in copyfile
    with open(src, 'rb') as fsrc, open(dst, 'wb') as fdst:
OSError: [Errno 22] Invalid argument: 'C:\\b\\s\\w\\ir\\x\\w\\install\\emscripten\\cache\\sysroot\\include\\png.h'
None
None
test_libpng (test_other.other) ... FAIL