patch sunriset.c so we can avoid main function

libs/sunriset/sunriset.c

@@ -128,7 +128,10 @@ double GMST0( double d );
 
 /* A small test program */
 
-main()
+#ifdef SUNRISET_NO_MAIN
+int sunriset_test_main(void) { return 0; }
+#else
+int main(void)
 {
       int year,month,day;
       double lon, lat;
@@ -234,6 +237,7 @@ main()
       return 0;
       }
 }
+#endif
 
 
 /* The "workhorse" function for sun rise/set times */