InstSimplify: Try to bring back the rest of r223583

This reverts r223624 with a small tweak, hopefully this will make stage3
equivalent.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223679 91177308-0d34-0410-b5e6-96231b3b80d8
[Hexagon] Adding add/sub with saturation.  Removing unused def.  Cleaning up shift patterns.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223680 91177308-0d34-0410-b5e6-96231b3b80d8
Lazily link GlobalVariables and GlobalAliases.

We were already lazily linking functions, but all GlobalValues can be treated
uniformly for this.

The test updates are to ensure that a given GlobalValue is still linked in.

This fixes pr21494.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223681 91177308-0d34-0410-b5e6-96231b3b80d8
Clean up the rst for the debug info tutorial

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223682 91177308-0d34-0410-b5e6-96231b3b80d8