This includes as little as possible in the assertion header, so
that it can be included globally in every file without pulling
any unwanted definitions. In particular pulling stdlib.h is
avoided because that can have side effects if it wants to
include non-portable extensions.
It is possible to have side-effects from include glib.h too, for
example because of G_LOG_DOMAIN.
These side-effects are usually avoidable with careful ordering
of pre-processor directives but with multiple levels of indirections
it can be hard to track. Better to make it robust to these kinds
of failures in the first place.
Also integrate with our logger for a cohesive experience (but
keep it a private dependency).
João Valverde