Flang tests are extremely slow on Windows

[Meinersbur]

@Endill

After all the PASS messages are printed for all the flang tests, a 20 minutes pause happens. The time is fairly consistent: 20 minutes minus 7-12 seconds. I believe this is the degradation we’ve been experiencing, or at least a major part of it.

This is consistent with the --timeout=1200 parameter reported by Mehdi. Some test is deadlocking or waiting for input?