Fix several issues in checking of address-of expressions.

 - clang was erroneously accepting address-of applied to lvalue
   expressions involving pointer arithmetic.
 - clang was erroneously rejecting address-of applied to deref
   expressions of pointer-typed variables.
 - Improved existing test case.
 - Fixes: <rdar://problem/6113867>, <rdar://problem/6080158>

llvm-svn: 54326