[MS-ABI] Implements MS-compatible RTTI

[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@209523 91177308-0d34-0410-b5e6-96231b3b80d8