Sema: Disallow taking the address of a bitfield coming from preincrement

Clang forgot that '++s.m' was a bitfield l-value and permit it's address
to be taken; this would crash at CodeGen-time.

Instead, propagate the object-kind when we see the prefix
increment/decrement.

This fixes PR20496.

Differential Revision: http://reviews.llvm.org/D4733