src/libpcp/src/derive_parser.y.in: be much more careful of oserror() use
src/libpcp/src/derive_parser.y.in: be much more careful of oserror() use

In BSD-land oserror() is likely to be a one-trip pony where the error
is reset soon after the call ... so calling it twice for the same
error code pat (e.g. to detect the error, then optionally to report
the error in a diagnostic) is bad form.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp