Makefile: add a missing build target for npc(1)

Makefile

@@ -17,7 +17,7 @@ CC=cc
 RUSTC=rustc
 
 .PHONY: all
-all: dj false fop hru intcmp mm rpn scrut str strcmp swab true
+all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
 
 build:
 	# keep build/include until bindgen(1) has stdin support
@@ -91,6 +91,12 @@ mm: build/bin/mm
 build/bin/mm: src/mm.c build
 	$(CC) $(CFLAGS) -o $@ src/mm.c
 
+
+.PHONY: npc
+npc: build/bin/npc
+build/bin/npc: src/npc.c build
+	$(CC) $(CFLAGAS) -o $@ src/npc.c
+
 .PHONY: rpn
 rpn: build/bin/rpn
 build/bin/rpn: src/rpn.rs build build/o/libsysexits.rlib