Make examples multiplatform

[illwieckz]

Now the examples build everywhere, not only on Windows.

I introduced some ifdef that may later be rewritten with deeper change by calling into some already implemented multiplatform functions from crnlib, or to implement such reusable multiplatform function, or to make them reusable, but I expect to do that in a second step, the same way I factorized the snprintf code after having made sure it was right.

[illwieckz]

I needed to add the -pthread flag to build the examples on the CI, actually linking the binaries without it didn't make sense.

For unknown reasons the build of crnlib/crunch was completing itself before without the flag but that's wrong, maybe some libs required by crnlib already implicitly required pthread.