The prescanner looks for implicit continuation lines when
there are unclosed parentheses at the end of a line, so that
source preprocessing macro references with arguments that span
lines are recognized. The condition that determines this
implicit continuation has been put into a predicate member
function and corrected to apply only when the following line
is source (not a preprocessing directive, comment, &c.).
Fixes bugzilla #46768.
Reviewed By: sscalpone
Differential Revision: https://reviews.llvm.org/D84280
320389e849