This ticket is to track this patch:

Mon Mar 21 17:02:34 EDT 2011  gwright at antiope.com
  * Debug output for OS X linker and coding standard upgrades
  
  This long an invasive patch tidies up the OS X linker and
  adds copious debugging output.  If ghci is invoked with +RTS -Dl -RTS,
  the result of every relocation and external symbol lookup is
  dumped in gory detail.  The resulting output is long, more than
  60 MB when starting ghci, even if no programs or packages are
  specified, but is very useful when hunting linker bugs.
  
  The coding standard changes are mostly to impose uniform whitespace
  convertions and to use curly braces even for one line if/else statement
  bodies.  I've been burned by lack of those a few times.

http://www.haskell.org/pipermail/cvs-ghc/2011-March/060538.html