DebugInfo: Track spilled variables in LiveDebugValues

DebugInfo: Track spilled variables in LiveDebugValues

When variables are spilled to the stack by the register allocator, keep track of their
debug locations in LiveDebugValues and insert DBG_VALUE instructions at the appropriate
place. Ensure that the locations are propagated down the dominator tree via the existing
mechanisms.

Reviewer: aprantl

Differential Revision: https://reviews.llvm.org/D29500

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294356 91177308-0d34-0410-b5e6-96231b3b80d8