use 100 minute timeout for azure mingw32 job

[mattip]

The Windows_mingw_gmake job is consistently timing out at the default 60 minutes. Add an explicit timeout and make it 100 minutes.

[mattip]

CI is passing, including azure. Looking at the logs, this is the first green CI run on azure since Dec 25.

Edit: the Dec 25 run was 58 minutes, the current run is 1hr4min. 100 minutes seems safe.

[martin-frbg]

Thanks - still annoying that it takes so long, but IIRC that's just mingw's way of handling files