I have become convinced that issuing -Wrestrict in gimple-fold
for calls to memcpy() where the source pointer is the same as
the destination causes more trouble than it's worth, especially
when inlining is involved, as in:

   inline void bar (void *d, void *s, unsigned N)
   {
     if (s != d)
       memcpy (d, s, N);
   }

   void foo (void* src)
   {
     bar (src, src, 1);
   }

It seems that there should be a way to teach GCC to avoid
folding statements in dead blocks (e.g., in a block controlled
by 'if (0 != 0)' as the one below), and that it might even speed
up compilation, but in the meantime it leads to false positive
-Wrestrict warnings.

The attached patch removes this instance of the warning and
adjusts tests not to expect it.

Martin