Merge branch 'js/drop-mingw-test-cmp'

Use `git diff --no-index` as a test_cmp on Windows.

We'd probably need to revisit "do we really want to, and have to,
lose CRLF vs LF?" later, at which time we may be able to further
clean this up by replacing "git diff --no-index" with "diff -u".

* js/drop-mingw-test-cmp:
  tests(mingw): avoid very slow `mingw_test_cmp`

diff --cc t/test-lib-functions.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge