sokol_app.h: trigger a linker error if users forget -pthread

[iboB]

My suggestion to resolve #455

[floooh]

Looks like good solution, thanks!

[floooh]

There's an error when compiled as C++:

/usr/include/pthread.h:470:12: error: conflicting declaration of ‘int pthread_yield()’ with ‘C’ linkage
 extern int pthread_yield (void) __THROW;
            ^~~~~~~~~~~~~

I'll include pthread.h instead and removed the manual declaration.

[floooh]

hmmmm it's not that simple... pthread.h doesn't contain pthread_yield() by default, instead _GNU_SOURCE must be defined before, but if there's already another include of pthread.h the _GNU_SOURCE define doesn't work. What a mess :/

My next attempt was calling pthread_self(), but for some reason this seems to be optimized away...

[iboB]

pthread_self (funny enough) doesn't actually require pthread to be linked. It's in libc.

And yeah, _GNU_SOURCE was the reason I just forward declared pthread_yield instead of including pthread.

As for C++, that's unpleasant. How about we keep the __THROW for now and in a couple of hours I'll find some time to submit a better solution in a PR?

[iboB]

Er... by the way won't adding "C" fix things properly? C functions should be nothrow

extern "C" int pthread_yield();

[floooh]

No worries, I found an okay-ish solution: pthread_attr_init/destroy works. It shows up in libsokol.a as external undefined symbol (unlike pthread_self()).

[floooh]

won't adding "C" fix things properly

Not sure, there's a lot of C++ specific stuff in /usr/include/pthread.h, and almost all functions are marked as __THROW.

[floooh]

Ok, see: 5fbb6a2