Tweak AdditionOverflowInLoaderExifJpeg for 32bit unsigned char OSes

Tweak AdditionOverflowInLoaderExifJpeg for 32bit unsigned char OSes

Last-Update: 2023-07-16
Forwarded: not-needed

AdditionOverflowInLoaderExifJpeg expects an overflow to happen on 32bit
architectures; due to the way LoaderExifJpeg & StringValueBase work and the
test data is fabricated, the overflow happens only architectures with signed
char.

Tweak AdditionOverflowInLoaderExifJpeg to account for this, by not expecting an
overflow in case the architecture has unsigned char (e.g. ARM and POWER).

For more discussion and notes, see: https://github.com/Exiv2/exiv2/issues/933

Gbp-Pq: Name tests-overflow-skip-unsigned-char-23bit.diff