Added enum for cc65 exit codes. replaced stdlib exit code names constants in libsrc with cc65 exit code named constants

libsrc/geos-common/common/_afailed.c

@@ -28,5 +28,5 @@ void _afailed (char* file, unsigned line)
 
     DlgBoxOk(CBOLDON "ASSERTION FAILED", "PROGRAM TERMINATED" CPLAINTEXT);
 
-    exit (2);
+    exit (CC65_EXIT_AFAILED);
 }

libsrc/geos-common/common/abort.c

@@ -6,10 +6,11 @@
 
 #include <stdlib.h>
 #include <geos.h>
+#include <cc65.h>
 
 void abort (void)
 {
     ExitTurbo();
     DlgBoxOk(CBOLDON "ABNORMAL PROGRAM", "TERMINATION." CPLAINTEXT);
-    exit(3);
+    exit(CC65_EXIT_ABORT);
 }