include: Add support for compilers which do not define __SIZEOF_INT__

__SIZEOF_INT__ is required by zephyr_stdint.h, however the __SIZEOF_*__
macros were only introduced in GCC 4.3.

This patch adds a work-around similar to that present in picolibc's
_default_types.h which attempts to guess the correct value of the
definition based on the value of __INT_MAX__ or from INT_MAX from
POSIX <limits.h> .

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>