[PATCH][BZ #16004] Check overlaps in memcpy_chk.

[Joseph S. Myers]

There are tests for *_chk functions in debug/.  If you add a new check you 
should also add testcases for it to confirm that the error is caught at 
runtime.  This does of course require also adding the same check to the 
generic version of the function, and in the case of memcpy_chk to the x86 
(32-bit) versions as well.

-- 
Joseph S. Myers
joseph@codesourcery.com