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