Thanks for the infos.
I will start ckecking, when i"m back at home sunday evening
also with __attrubute__((packed))
The change was used for bootstrap compile
of Open-Watcom-v2 on x86_64-linux with tcc
as an alternative to gcc or clang.
One of the "unaligned" variants is used in the OpenWatcom source.
Microsoft MSVC supports both variants and ARMasm at least one version.
Of course, OpenWatcom supports this also.
I can remember, that in a recent OpenWatcon dev session,
my grep for 'undefined' in the tcc root directory files found nothing
and with the patched tcc, bootstrap of OpenWatcom continues.
Normally, i use git grep, and that would have detected
the use in "_mingw.h".