fcntl: open should use a va_list

The current implementation of open requires the user to pass all three
args to the function. It should use a va_list and allow a user to
provide only the filename and flags.

include/bits/fcntl.h

@@ -0,0 +1,13 @@
+#ifndef _BITS_FCNTL_H
+#define _BITS_FCNTL_H
+
+int open(const char* filename, int flags, ...) {
+    mode_t mode = 0;
+	va_list ap;
+	va_start(ap, flags);
+    mode = va_arg(ap, mode_t);
+	va_end(ap);
+    return sys_open(filename, flags, mode);
+}
+
+#endif