return LIBAVRDUDE_EXIT instead of exit(0)

src/libavrdude.h

@@ -59,6 +59,7 @@ typedef uint32_t pinmask_t;
 #define LIBAVRDUDE_NOTSUPPORTED (-2) // operation not supported
 #define LIBAVRDUDE_SOFTFAIL (-3) // returned, eg, by avr_signature() if caller
                                  // might proceed with chip erase
+#define LIBAVRDUDE_EXIT (-4)     // End all operations in this session
 
 /* formerly lists.h */
 

src/linuxspi.c

@@ -417,7 +417,7 @@ static int linuxspi_parseextparams(const PROGRAMMER *pgm, const LISTID extparms)
       msg_error("%s -c %s extended options:\n", progname, pgmid);
       msg_error("  -xdisable_no_cs Do not use the SPI_NO_CS bit for the SPI driver\n");
       msg_error("  -xhelp          Show this help menu and exit\n");
-      return LIBAVRDUDE_SOFTFAIL;
+      return LIBAVRDUDE_EXIT;
     }
 
     pmsg_error("invalid extended parameter '%s'\n", extended_param);