build: also reject invalid options when fetching

[JohannesKauffmann]

This avoids fetching for a long time, and then realising that the options given are invalid.

[niXman]

im sorry, but I can't accept this PR because it will broke fetch-only mode.

[JohannesKauffmann]

Can you elaborate how it will break fetch mode? From my point of view, it doesn't make sense to try to fetch sources for a configuration that is invalid.

As it stands right now, an invalid options configuration is accepted when only fetching, but gets rejected when trying to build. So why not reject it in the first place?

[niXman]

ah, right! the architecture+exceptions+threads_model+CRT_type must always be checked!

sorry, approved.

[JohannesKauffmann]

Thank you!