gallium,util: undef ALIGN on FreeBSD to prevent name clash

Some rare headers like ipc/shm and pthread_np cause
machine/param.h to be included which defines a macro called ALIGN.

Signed-off-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3559>

src/util/u_thread.h

@@ -45,6 +45,10 @@
 #endif
 
 #ifdef __FreeBSD__
+/* pthread_np.h -> sys/param.h -> machine/param.h
+ * - defines ALIGN which clashes with our ALIGN
+ */
+#undef ALIGN
 #define cpu_set_t cpuset_t
 #endif