Decided to re-run this test, as it's been a while. I've been applying the patch before my normal test runs, so I haven't checked for its (continued) failure for a while. Given that my test results have been consistent across all test sets, I doubt I've got something wrong with my env setup during testing.
Note that if I run this test with runner.rb in a windows env, the test passes. But as noted below, it fails when run with make (I set a make env by adding msys64\mingw64\bin and msys64\usr\bin to my path.)
PATH must keep library loading paths on a platform where it is
used for that purpose, for extra libraries.
[ruby-core:81178] [Bug #13569] [Fix GH-1616]