Enable -Wcpp-undef in Hadrian
In !6340 (closed), @doyougnu reports:
The panics were caused by
#ifdef UNIQUE_TAG_BITS == 8
evaluating to theelse
branch even on 64-bit machines. Which was due to the missing#include Unique.h
which definesUNIQUE_TAG_BITS
.
It should have been easier to spot. We should pass -Wcpp-undef
in Hadrian.