x86-64: Use notl in EVEX strcmp [BZ #28646]

Must use notl %edi here as lower bits are for CHAR comparisons
potentially out of range thus can be 0 without indicating mismatch.
This fixes BZ #28646.

Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 4df1fa6d)