[Qbs] Using ConanfileProbe with yocto cross compiling toolchain

[Richard Weickelt]

> I archived my goal with the following code:

Good to hear. Thanks for posting the code.

> But this code has some restrictions (like using bash or zsh but not fish).

I wouldn't consider it a restriction not to support an exotic shell.

> Thus I don't think that it should be made into the official Qbs codebase.
> Maybe this code could be used in some How-To section or something.

What's your experience in using Qbs with Yocto? Once you solved the
EnvironmentScriptProbe, were there a lot of additional steps needed? Any
pitfalls? I guess a howto would be nice in general and might be interesting
for some people. On the other hand - and without having much knowledge about
yocto - how high is the risk that this howto would be outdated by tomorrow?

> If you really want me to contribute this as a "YoctoEnvironmentProbe",
> despite the restrictions, I will do some cleanup an contribute it.

Probing exported environment variables from a shell script deserves a
generic probe. If you could make it work for .bat and ps1 as well, even
better. Don't forget to add a testcase in test_blackbox.cpp.

Thank you for you contribution.