I'm not sure D104465 (the motivation for this patch) is the right approach, but we can have that discussion over there.
Why turn this on all the time? That adds a lot of noise below. Can you instead just turn it on for specific targeted tests?
Also, maybe I just missed it, but I don't see any tests that check the behaviour of this flag.
I'm uncomfortable dropping the check that #define MACRO\n\n\n turns into precisely #define MACRO\n.