[Bug preprocessor/60723] Line directives with incorrect system header flag

[nicholas.ormrod at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60723

--- Comment #7 from Nicholas <nicholas.ormrod at hotmail dot com> ---
What a pleasant surprise to see your name, Matt.

This dropped off my radar for a bit, but I'm pretty close now to getting a
properly organized patch ready. Details to follow within 5 days.