Bug 475652 - Missing suppression for __wcsncpy_avx2 (strncpy-avx2.S:308)?

Bug 475652 - Missing suppression for __wcsncpy_avx2 (strncpy-avx2.S:308)?

Adds a replace strmem wrapper for wcsncpy

Whilst doing this I noticed that

memcheck/tests/filter_memcheck

wasn't filtering memcheck/tests/freebsd/timingsafe properly.
That's because before filtering vg_replace_strmem.c and
vg_replace_malloc.c there's a check that the test exe filename
does not match the line. In this case the test exe was "timingsafe",
but line contained "timingsafe_memcmp", which matched leaving
vg_replace_strmem.c unfiltered. So I just renamed the testcase.