Update to SDCC 3.5.0

- Replace make_labels with sed script, because the map file format
changed.
- Remove __fastcall__ in the single place where it was still present
(leftover from CC65)
- Use __z88dk_fastcall where possible in the conio driver, speeding up
drawing a little further.
- Allow "unsafe reads" since we don't have any read-sensitive IO mapped
in memory space.

There changes free an extra 900 bytes of RAM, making us closer to 25K
RAM free (with memstat runnning).
diff --git a/contiki-cpc/apps/configedit.c b/contiki-cpc/apps/configedit.c
index 5d43f72..ec672f4 100644
--- a/contiki-cpc/apps/configedit.c
+++ b/contiki-cpc/apps/configedit.c
@@ -197,7 +197,7 @@
   return nt;
 }
 /*-----------------------------------------------------------------------------------*/
-static char * __fastcall__
+static char *
 copystr(char *dst, char *src, int len)
 {
   char *nt = nullterminate(src);