[PATCH] C undefined behavior fix

[dewar@gnat.com]

>>Isn't the incriminated construct already outside of C and non-portable?

The issue is not whether it is outside standard-C here, which of course
it is, but rather whether there is some extension to GNU-C (either an
interpretation of undefined or implementation defined, or an attribute etc)
which wuld make it inside GNU-C even if outside C, and therefore portable
to GNU-C, which is good enough for this purpose.