cpu: Include common.h for av_popcount64

This fixes build failures on windows since 2a6eaeaa.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/cpu.c

@@ -19,6 +19,7 @@
 #include "cpu.h"
 #include "config.h"
 #include "opt.h"
+#include "common.h"
 
 #if HAVE_SCHED_GETAFFINITY
 #define _GNU_SOURCE