testprogs: Add missing libm.h includes

This fixes building on MSVC 2010 and 2012 after d12b5b2f.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/iirfilter-test.c

@@ -20,6 +20,8 @@
 #include <stdint.h>
 #include <stdio.h>
 
+#include "libavutil/libm.h"
+
 #include "iirfilter.h"
 
 #define FILT_ORDER 4

libavutil/eval-test.c

@@ -20,6 +20,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "libm.h"
 #include "timer.h"
 #include "eval.h"