Merge branch 'sk/mingw-tests-workaround'

Make tests pass on msysgit by mostly disabling ones that are
infeasible on that platform.

* sk/mingw-tests-workaround:
  t800[12]: work around MSys limitation
  t9902: mingw-specific fix for gitfile link files
  t4210: skip command-line encoding tests on mingw
  MinGW: disable legacy encoding tests
  t0110/MinGW: skip tests that pass arbitrary bytes on the command line
  MinGW: Skip test redirecting to fd 4