Fix <bitsize.h>

diff --git a/klibc/open.c b/klibc/open.c
index 7a6a529..cb1f519 100644
--- a/klibc/open.c
+++ b/klibc/open.c
@@ -8,6 +8,7 @@
 #define _KLIBC_IN_OPEN_C
 #include <unistd.h>
 #include <fcntl.h>
+#include <bitsize.h>
 
 #if _BITSIZE == 32 && !defined(__i386__)