Remove some warnings from tests

Remove some warnings from tests

Various tests do things which we want to detect at runtime, like
ignoring the result of malloc or doing a deliberate impossibly large
allocation or operations that would result in overflowing or
truncated strings, that generate a warning from gcc.

In once case, mq_setattr called with new and old attrs overlapping,
this was explicitly fixed, in others -Wno-foobar was added to silence
the warning. This is safe even for older gcc, since a compiler will
ignore any -Wno-foobar they don't know about - since they do know they
won't warn for foobar.