Move macro.h to shared directory

It's not really related to libkmod, so move it to a directory in which
we keep common stuff.
diff --git a/tools/rmmod.c b/tools/rmmod.c
index df2f041..8a3c22e 100644
--- a/tools/rmmod.c
+++ b/tools/rmmod.c
@@ -26,7 +26,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include "libkmod.h"
-#include "macro.h"
+#include <shared/macro.h>
 
 #include "kmod.h"