Finalize update t SDCC 4.2

Overall a gain of 2K of memory, not bad at all!
diff --git a/contiki-cpc/arch/arch.c b/contiki-cpc/arch/arch.c
index b090326..48facc4 100644
--- a/contiki-cpc/arch/arch.c
+++ b/contiki-cpc/arch/arch.c
@@ -8,11 +8,7 @@
 	return _clock_val;
 }
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <ctype.h>
-
 int ctk_arch_isprint(char c)
 {
-	return isprint(c);
+	return (unsigned char)c > 32;
 }