MesaLib fails to compile on Linux

[leeplusplus%protonmail.com@localhost]

Hello everyone,

I'm still getting used to pkgsrc, so I apologize if my question seems silly. I have been testing out pkgsrc recently, and I tried compiling SuperTux as a test. However, it (and a few other games) depends on MesaLib, which won't compile for me.

I keep getting these errors when it tries to compile it:

../include/c11/threads_posix.h:69:25: error: conflicting types for 'once_flag'; have 'pthread_once_t' {aka 'int'}
   69 | typedef pthread_once_t  once_flag;
      |                         ^~~~~~~~~

../include/c11/threads_posix.h:94:1: error: conflicting types for 'call_once'; have 'void(int *, void (*)(void))'
   94 | call_once(once_flag *flag, void (*func)(void))
      | ^~~~~~~~~

Does anyone have any idea why? I am using a pretty standard Gentoo install with OpenRC.

-Lee