Build EC's for globals twice. The first is after constructing the initial

Globals Graph for the local pass, the second is after all of the locals
graphs have been constructed.  This allows for many additional global EC's
to be recognized that weren't before.  This speeds up analysis of programs
like 177.mesa, where it changes DSA from taking 0.712s to 0.4018s.

llvm-svn: 20711