Add to the split module utility an SCC based method which allows not to globalize any local variables.

Summary:
Currently llvm::SplitModule as the first step globalizes all local objects, which might not be desirable in some scenarios.
This change adds a new flag to llvm::SplitModule that uses SCC approach to search for a balanced partition without the need to externalize symbols.
Such partition might not be possible or fully balanced for a given number of partitions, and is a function of the module properties (global/local dependencies within the module).

Joint development Tobias Edler von Koch (tobias@codeaurora.org) and Sergei Larin (slarin@codeaurora.org)

Subscribers: llvm-commits, joker.eph

Differential Revision: http://reviews.llvm.org/D16124