configure: Use -fno-strict-aliasing -fno-strict-overflow
Contemporary compilers can squeeze out some extra performance by
assuming the program never executes code that has undefined behavior
according to the C standard. Unfortunately, this can break programs.
Pointing out that these programs are non-conforming is as correct as
it is unhelpful, at least as long as the compiler is unable to
diagnose the non-conformingness.
Since keeping our programs working is a lot more important to us than
running them as fast as possible, forbid some assumptions that are
known to break real-world programs:
* Aliasing: perfectly clean programs don't engage in type-punning, and
perfectly conforming programs do it only in full accordance with the
standard's (subtle!) aliasing rules. Neither kind of perfection is
realistic for us, therefore -fno-strict-aliasing.
* Signed integer overflow: perfectly clean programs won't ever do
signed integer arithmetic that overflows. This is an imperfect
program, therefore -fno-strict-overflow.
Signed-off-by: Markus Armbruster <armbru@pond.sub.org>