Introduce the "@llvm.dbg.value" debug intrinsic.

Introduce the "@llvm.dbg.value" debug intrinsic.

The semantics of llvm.dbg.value are that starting from where it is executed, an offset into the specified user source variable is specified to get a new value.

An example:
  call void @llvm.dbg.value(metadata !{ i32 7 }, i64 0, metadata !2)
Here the user source variable associated with metadata #2 gets the value "i32 7" at offset 0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90788 91177308-0d34-0410-b5e6-96231b3b80d8