Always activate `__USE_MINGW_ANSI_STDIO` unless overridden on the command
line. This is necessary with older versions of MingW and/or Windows,
where snprintf does not always zero-terminate the buffer, and does
not support formats such as `"%zu"` for size_t and `"%lld"` for long long.
Simplify debug.h accordingly. The macros `MBEDTLS_PRINTF_SIZET`,
`MBEDTLS_PRINTF_SIZET_HAX` and `MBEDTLS_PRINTF_LONGLONG` are no longer
needed, but they are still used in our code base and must stay in debug.h
for backward compatibility.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>