Add 1994/imc/try.sh + inclusion of unistd.h

The inclusion of unistd.h is for getpid(2). While not strictly necessary
(at least not observed) this type of thing can be a problem and in some
other entries a missing or incorrect prototype caused the entry to fail
(sometimes only some systems namely macOS). This was just noticed by
chance and I did it on a whim.

1994/imc/imc.c

@@ -1,5 +1,6 @@
 #include<stdio.h>
 #include<stdlib.h>
+#include<unistd.h>
 #define f (sizeof(int))
 
 int i,j,k,l,m,*t,*u,*v;