build 8.8.1 with 8.8.1 fails with -DSTAGE=1
ghc-8.8.1 fails to build self, because with -DSTAGE=1 it can't get TAG_MASK from MachDeps.h
(ghc-8.6.3 works, but just because it doesn't pass the -DSTAGE=1 to gcc.)
Steps to reproduce
Build and install 8.8.1. Use it to build 8.8.1 again from scratch.
Die on stage 1, compiler/parser/cutils.c TAG_MASK undefined in ClosureMacros.h
(I don't really expect that, since I'm sure this has been done numerous times with no problem, but it's what happened here, and the way it works - only 8.8.1 passes -Xpreprocessor '-DSTAGE=1' to gcc - has me quite baffled.)
Related to issue #16797