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.)
I can reproduce this with msys2 build.
miniruby.exe and ruby.exe have dependency to libgmp-10.dll.
So path which contains libgmp-10.dll is needed to PATH environment variable.
I can avoid the issue by copying libgmp-10.dll to current directory.
test/ruby/test_rubyoptions.rb (TestRubyOptions#test_search):
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]