Implement new LibCallSimplifier class

This patch implements the new LibCallSimplifier class as outlined in [1].
In addition to providing the new base library simplification infrastructure,
all the fortified library call simplifications were moved over to the new
infrastructure.  The rest of the library simplification optimizations will
be moved over with follow up patches.

NOTE: The original fortified library call simplifier located in the
SimplifyFortifiedLibCalls class was not removed because it is still
used by CodeGenPrepare.  This class will eventually go away too.

[1] http://lists.cs.uiuc.edu/pipermail/llvmdev/2012-August/052283.html

llvm-svn: 165873