Fix conditional compilation not skipping #emit directives

#emit directives inside #if ... #endif blocks were processed by the
compiler regardless of the condition.

--------- test code --------

main() {
	#if 0
		#emit halt 1
	#endif
}

----- end of test code -----

source/compiler/sc2.c

@@ -1228,6 +1228,7 @@ static int command(void)
     break;
 #if !defined NOEMIT
   case tpEMIT: {
+    if (!SKIPPING) {
       /* write opcode to output file */
       char name[40];
       int i;
@@ -1294,6 +1295,7 @@ static int command(void)
       } /* if */
       stgwrite("\n");
       check_empty(lptr);
+    } /* if */
     break;
   } /* case */
 #endif