Fix tr/// determination of inplace editing for EBCDIC

Fix tr/// determination of inplace editing for EBCDIC

I realized as a result of fixing GH #17654, that the code didn't
properly decide if a tr/// can be done in-place on EBCDIC platforms.
Since we didn't have an EBCDIC smoker at the time, I couldn't be sure
that the fix actually worked.  Now that we do have a smoker, I have
successfully tested it.

This patch is constructed so that the code generated on non-EBCDIC
platforms should not be changed by it.