portability macro flags updates, for Haiku

portability macro flags updates, for Haiku

some non-trivial changes to platform.h and util.h,
initially related to compilation for Haiku,
but I used this opportunity to make them cleaner
and add some documentation.

Noticed several tests that could be improved
(too harsh conditions, useless exception, etc.)
but I did not dare modifying too many tests just before release.