Uppercase hex number conversions fail for abtol, strtol, strtoul,
strtoull, atoi, and abtod.
The following patch fixes it. This allows tcc to handle assembly
language, which is necessary to build the Fiwix kernel as part of the
kernel bootstrapping in progress for the live-bootstrap project.
* lib/ctype/isxdigit.c (isxdigit): Also allow A-F.
* lib/mes/abtol.c (abtol): Also cater for A-F.