Error running make check-fast on Windows

[schmee]

After failing to build Rust on Windows with make check, as reported in #15250, I saw in the wiki that make check-fast is the recommended way to run the tests on Windows. So I gave it a shot, but still no dice! This time, it is the unit tests in libglob\lib.rs that fails.

The error happens when building master on commit 04da31e64c983ff49234104b79133d4981ea3314.

Error

rustc: i686-pc-mingw32/stage2/test/globtest-i686-pc-mingw32.exe
run: i686-pc-mingw32/stage2/test/globtest-i686-pc-mingw32.exe

running 12 tests
test test::test_matches_path ... ok
test test::test_pattern_matches ... ok
test test::test_pattern_matches_require_literal_leading_dot ... ok
test test::test_pattern_matches_case_insensitive ... ok
test test::test_pattern_escape ... ok
test test::test_wildcard_optimizations ... ok
test test::test_lots_of_files ... FAILED
test test::test_pattern_matches_require_literal_separator ... ok
test test::test_range_pattern ... ok
test test::test_pattern_matches_case_insensitive_range ... ok
test test::test_unclosed_bracket ... ok
test test::test_absolute_pattern ... ok

metrics saved to: tmp\check-stage2-T-i686-pc-mingw32-H-i686-pc-mingw32-glob-metrics.json
failures:

---- test::test_lots_of_files stdout ----
        task 'test::test_lots_of_files' failed at 'rust_list_dir_wfd_fp_buf returned invalid UTF-16', C:\msys64\home\John\programming\forks\rustmain\rust\src\libcore\option.rs:246



failures:
    test::test_lots_of_files

test result: FAILED. 11 passed; 1 failed; 0 ignored; 0 measured

task '<main>' failed at 'Some tests failed', C:\msys64\home\John\programming\forks\rustmain\rust\src\libtest\lib.rs:243
/home/John/programming/forks/rustmain/rust/mk/tests.mk:443: recipe for target 'tmp/check-stage2-T-i686-pc-mingw32-H-i686-pc-mingw32-glob.ok' failed
make: *** [tmp/check-stage2-T-i686-pc-mingw32-H-i686-pc-mingw32-glob.ok] Error 101

[schmee]

cc @alexcrichton