run-tests: add a --compiler option Without this option, it is not possible to run the test suite on Windows using mingw's gcc as the compiler.

run-tests: make build command line less intimidating Use a dict for parameters to the format string, instead of a ridiculous number of positional parameters.

hooks: be even more forgiven of non-fd descriptors (issue3711) Looks like there are instances where sys.stdout/stderr contain file handles that are invalid. We should be tolerant of this for hook I/O redirection, as our primary concern is not garbling our own output stream.

hooks: delay I/O redirection until we actually run a hook (issue3711) We were attempting to redirect I/O even if no hook was actually getting called. This defers redirection until we've found something to do.