[Bug libfortran/67540] string_intrinsics_inc.c sanitizer detects null pointer passed to memcpy

[zeccav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67540

--- Comment #7 from Vittorio Zecca <zeccav at gmail dot com> ---
str4 used to point to str so the "logic" seems to check that str4 does
not follow any more str.
But the test is erroneous.