[ms-inline asm] Extend the Sema interface to get the size and length of a
VarDecl.
Part of rdar://12576868

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172742 91177308-0d34-0410-b5e6-96231b3b80d8
[ms-inline asm] Updates and test case for r172743.
Part of rdar://12576868

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172744 91177308-0d34-0410-b5e6-96231b3b80d8