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/Makefile

@@ -38,8 +38,7 @@ include ../../var.mk
 
 # Common C compiler warnings to silence
 #
-CSILENCE= -Wno-error -Wno-implicit-function-declaration \
-	-Wno-deprecated-non-prototype -Wno-strict-prototypes
+CSILENCE= -Wno-error -Wno-deprecated-non-prototype -Wno-strict-prototypes
 
 # Common C compiler warning flags
 #