Split TargetLowering into a CodeGen and a SelectionDAG part.

This fixes some of the cycles between libCodeGen and libSelectionDAG. It's still
a complete mess but as long as the edges consist of virtual call it doesn't
cause breakage. BasicTTI did static calls and thus broke some build
configurations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172246 91177308-0d34-0410-b5e6-96231b3b80d8
Added debug messages to GlobalOpt.

Specifically:
1. Added a missing new line when we emit a debug message saying that we are marking a global variable as constant.
2. Added debug messages that describe what is occuring when GlobalOpt is evaluating a block/function.
3. Added a debug message that says what specific constructor is being evaluated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172247 91177308-0d34-0410-b5e6-96231b3b80d8
Remove some accidentaly duplicated code. This needs urgent cleanup :(

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172248 91177308-0d34-0410-b5e6-96231b3b80d8