I have built "in the official manner" both GHC 7.8.4 and GHC 7.10.1 rc2 from sources. You can find them here:
They need some "doesn't crash out of the box" testing on a few OS X systems before I think we should declare them good and put them on the download page.
Can you help out?
Basic instructions to install a bindist in a local, isolated area (so you don't clobber your system GHC installation):
mkdir test-ghc
cd test-ghc
tar xf $binddist_tar_file
cd ghc*
configure --prefix=`cd ..; pwd`
make install
cd ..
Let me know if that works - and what version of OS X you used.