Plan should build with GCC.

src/Makefile

@@ -1,10 +1,10 @@
 plan:
 	dtrace -h -s plan_probes.d
-	cc -c plan_manip.c
-	cc -c plan_main.c
-	cc -c plan_atomic.c
+	gcc -c plan_manip.c
+	gcc -c plan_main.c
+	gcc -c plan_atomic.c
 	dtrace -G -32 -s plan_probes.d plan_manip.o plan_main.o plan_atomic.o
-	cc -o plan plan_main.o plan_manip.o plan_atomic.o plan_probes.o -lumem -ldtrace
+	gcc -o plan plan_main.o plan_manip.o plan_atomic.o plan_probes.o -lumem -ldtrace
 
 clean:
 	rm plan_main.o

src/plan_impl.h

@@ -40,6 +40,7 @@
 #define	NEXT	2
 
 typedef enum day {
+	NEGDAY = -1,	/* force day_t to be signed, GCC/SunCC diff */
 	SUN,
 	MON,
 	TUES,

src/plan_manip.c

@@ -1354,6 +1354,7 @@ list(day_t d, tm_t *date, int flag, int nl)
 	int dfd;
 	int have_date;
 
+
 	if (!date && d <= -1) {
 		exit(0);
 	}