[MS-ABI] Implements MS-compatible RTTI
Enables the emission of MS-compatible RTTI data structures for use with
typeid, dynamic_cast and exceptions.  Does not implement dynamic_cast
or exceptions.  As an artiface, typeid works in some cases but proper
support an testing will coming in a subsequent patch.

majnemer has fuzzed the results.  Test cases included.

Differential Revision: http://reviews.llvm.org/D3833