Improve llvm.dbg.declare intrinsic by referring directly to the storage in its first...

Improve llvm.dbg.declare intrinsic by referring directly to the storage in its first argument, via function-local metadata (instead of via a bitcast).
This patch also cleans up code that expects there to be a bitcast in the first argument and testcases that call llvm.dbg.declare.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93504 91177308-0d34-0410-b5e6-96231b3b80d8