games/prboom: fix build in 14

Fix bompilation problem on FreeBSD 14:

    i_system.c:444:7: error: unknown type name 'cpu_set_t'; did you mean 'cpusetid_t'?
          cpu_set_t set;
          ^~~~~~~~~

Approved by:	portmgr blanket

games/prboom/files/patch-src_SDL_i__system.c

@@ -0,0 +1,19 @@
+--- src/SDL/i_system.c.orig	2008-11-09 18:19:11 UTC
++++ src/SDL/i_system.c
+@@ -72,6 +72,7 @@
+ #include <fcntl.h>
+ #include <sys/stat.h>
+ #include <errno.h>
++#include <sys/cpuset.h>
+
+ #ifndef PRBOOM_SERVER
+ #include "m_argv.h"
+@@ -441,7 +442,7 @@ void I_SetAffinityMask(void)
+     // POSIX version:
+     int i;
+     {
+-      cpu_set_t set;
++      cpuset_t set;
+
+       CPU_ZERO(&set);
+