How do you build the haddocks for a boot library?

Hi, I have some changes to the haddocks in ghc-prim which are re-exported from base. In order to check that I got the syntax right I've tried to build the haddocks by following https://ghc.haskell.org/trac/ghc/wiki/Building/Docs#Haddockdocumentation. Sadly, when I run "make html" in libraries/ghc-prim or libraries/base I get the following error: GNUmakefile:3: libraries/ghc-prim/mk/sub-makefile.mk: No such file or directory make: *** No rule to make target 'libraries/ghc-prim/mk/sub-makefile.mk'. Stop. What should I do instead? Cheers, Simon