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 275079e3adc184ba3841222918e852c3e63f435f)
diff --git a/meson.build b/meson.build
index c2843a3..9fc09a4 100644
--- a/meson.build
+++ b/meson.build
@@ -1354,7 +1354,7 @@
 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>',