retval(1) sans documentation

Makefile

@@ -32,7 +32,7 @@ RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
-all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
+all: dj false fop hru intcmp mm npc retval rpn scrut str strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
@@ -122,6 +122,11 @@ npc: build/bin/npc
 build/bin/npc: src/npc.c build
 	$(CC) $(CFLAGAS) -o $@ src/npc.c
 
+.PHONY: retval
+retval: build/bin/retval
+build/bin/retval: src/retval.rs build rustlibs
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/retval.rs
+
 .PHONY: rpn
 rpn: build/bin/rpn
 build/bin/rpn: src/rpn.rs build rustlibs