add exitcode

src/lib9/exitcode.c

diff --git a/src/lib9/exitcode.c b/src/lib9/exitcode.c
new file mode 100644
index 0000000..f65836e
--- /dev/null
+++ b/src/lib9/exitcode.c
@@ -0,0 +1,9 @@
+#include <u.h>
+#include <libc.h>
+
+int
+exitcode(char *s)
+{
+	return 1;
+}
+

src/lib9/mkfile

diff --git a/src/lib9/mkfile b/src/lib9/mkfile
index 556be2f..a244dd3 100644
--- a/src/lib9/mkfile
+++ b/src/lib9/mkfile
@@ -99,6 +99,7 @@
 	errstr.$O\
 	exec.$O\
 	execl.$O\
+	exitcode.$O\
 	fcallfmt.$O\
 	get9root.$O\
 	getcallerpc-$OBJTYPE.$O\