#3823 SDCDB source not valid C23

[Philipp Klaus Krause]

I've tried compiling SDCC as C23, to prepare for GCC 15 making C23 the default.

Despite using "make -k ", I can't progress beyond failing attempts to compile sdcdb and asxxxx. The latter is probably something to look into after merging current upstream asxxxx into our fork.

For sdcdb, we fail at

sdcdb.h:63:15: error: both ‘short’ and ‘_Bool’ in declaration specifiers
   63 | typedef short bool;

I don't think we need sdcdb to be able to compile with pre-C99 compilers, so we after checking that two values are enough for bool, we could just use #include <stdbool.h> and remove the typedef?

[Philipp Klaus Krause]

Fixed in [r15567].