[Bug c/61593] Support '#pragma mark - foo' (by simply ignoring it without warning)

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61593

--- Comment #1 from Eric Gallager <egall at gwmail dot gwu.edu> ---
The gcc documentation says pragma mark should be accepted:
https://gcc.gnu.org/onlinedocs/gcc/Darwin-Pragmas.html#Darwin-Pragmas