Enhance the TD pass to build composite graphs when we have indirect call

sites that target multiple callees.  If we have a function table, for
example, with N callees, and M callers call through it, we used to have
to perform O(M*N) graph inlinings.  Now we perform O(M+N) inlinings.

This speeds up the td pass on perlbmk from 36.26s to 25.75s.

llvm-svn: 20743