[patch] libstdc++/66327 don't pass null pointers to memcmp

[Jörg Richter]

Jonathan Wakely <jwakely <at> redhat.com> writes:

> This is a rather brute force fix, but if noone has any better ideas
> I'll commit this to the trunk and 4.9 and 5 branches tomorrow. (I
> think it should go on the branches, because 4.9 is known to optimise
> away null pointer checks after invalid calls to memcmp like this).

How about comparing only the length against 0? 
The pointers must be != 0 if length > 0.

- Jörg