Trying to consolildate #11065 and #11019 to hopefully get it merged.
In short, the new xrOS sdk defines the folowing in types.h:

#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#include <sys/_types/_u_char.h>
#include <sys/_types/_u_short.h>
#include <sys/_types/_u_int.h>
#ifndef _U_LONG
typedef unsigned long           u_long;
#define _U_LONG
#endif
typedef unsigned short          ushort;         /* Sys V compatibility */
#ifndef __DARWIN_UINT
typedef unsigned int            uint;           /* Sys V compatibility */
#define __DARWIN_UINT
#endif
#endif

So I added _DARWIN_C_SOURCE for the visionOS build which seems to work, alternative would be to include _u_int etc in every file but that seems like a less viable solution. I don't think there's any reason to not have _DARWIN_C_SOURCE defined, I have only added the define for visionOS anyway since it seems to only be a problem with those SDK headers