I got a fresh copy of HEAD today, and the build failed. The failing command is: 

$ cd libraries && sh gen_contents_index --intree
haddock: internal error: /Users/andreas/repos/temp-ghc-2/ghc-build/inplace/lib/html/Ocean.std-theme/hslogo-16.png: copyFile: does not exist (No such file or directory)

I have not yet had time to look into this, but hopefully someone knows what happened here. 

-Andi