util: Avoid pthread_setaffinity_np on NetBSD

NetBSD's variant has a different prototype from the Linux version
the code expects. It might make sense to add support for NetBSD's
version, however, since NetBSD defaults to not allowing non-root
users to set processor affinity, there would be little gain here.

This is a build fix for NetBSD.

Signed-off-by: Nia Alarie <nia@NetBSD.org>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
CC: 20.3 <mesa-stable@lists.freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7947>
(cherry picked from commit 275079e3ad)

.pick_status.json

@@ -1381,7 +1381,7 @@
         "description": "util: Avoid pthread_setaffinity_np on NetBSD",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },

meson.build

@@ -1354,7 +1354,7 @@ endif
 dep_thread = dependency('threads')
 if dep_thread.found() and host_machine.system() != 'windows'
   pre_args += '-DHAVE_PTHREAD'
-  if cc.has_function(
+  if host_machine.system() != 'netbsd' and cc.has_function(
       'pthread_setaffinity_np',
       dependencies : dep_thread,
       prefix : '#include <pthread.h>',