Don't raise Wide char warning in UTF-8 locale

Don't raise Wide char warning in UTF-8 locale

This belongs in the category of "I can't believe I did that."  Commit
613abc6d16e99bd9834fe6afd79beb61a3a4734d introduced warning messages
when a multi-byte character is operated on in a single byte locale.  But
the two macros introduced fail to suppress said messages when in a
multi-byte locale where the operation is perfectly valid.

This partially solves v5.22 blocker [perl #123527].  But it could still
fail if the test files are called from within a non-UTF-8 locale.  I
will issue a pull request for fixing that.