Don't report unclosed comments as "no newline at end of file". If we get EOF in the "middle" of a line but there's a newline at the end of the buffer we've got, it's because we're in the middle of a comment. So, say so.

#define BC //**/*
#define EC */**//

BC
comment?
EC

BC comment? EC

#define FOO(x) x
FOO(abc BC def EC ghi)

#define BAR(x, y) x y
BAR(abc BC def, ghi EC jkl)

BC
#define BAZ baz
EC
BAZ