Need to compile strdup.c; this script probably ought to be generated.

src/mkmk.sh

diff --git a/src/mkmk.sh b/src/mkmk.sh
index 37c4392..7d6b865 100644
--- a/src/mkmk.sh
+++ b/src/mkmk.sh
@@ -72,6 +72,7 @@
 9c  seek.c
 9c  sendfd.c
 9c  sleep.c
+9c  strdup.c
 9c  strecpy.c
 9c  sysfatal.c
 9c  sysname.c