Is everyone telling me, (by inference) that modern compilers produce
run-time code that actually cares, in a formatted read, about the difference
between (traditional) cr-lf double symbol and single symbol cr or lf
line-ending codes? (ie among these three tokens for line-end?).

That would be a crazy system design criteria to not include and accept all
three variants.
I know my trusty 1985 compiler producses code that handles all three; and I
haven't noticed any problem with my DVF 6.6c compiler either. Why don't the
new run-time codes?

When I parse text (from unformatted reads) I look for all three variants
too. It isn'r exactly rocket science.