MS ABI: Implement support for throwing a C++ exception

MS ABI: Implement support for throwing a C++ exception

Throwing a C++ exception, under the MS ABI, is implemented using three
components:
- ThrowInfo structure which contains information like CV qualifiers,
  what destructor to call and a pointer to the CatchableTypeArray.
- In a significant departure from the Itanium ABI, copying by-value
  occurs in the runtime and not at the catch site.  This means we need
  to enumerate all possible types that this exception could be caught as
  and encode the necessary information to convert from the exception
  object's type to the catch handler's type.  This includes complicated
  derived to base conversions and the execution of copy-constructors.

N.B. This implementation doesn't support the execution of a
copy-constructor from within the runtime for now.  Adding support for
that functionality is quite difficult due to things like default
argument expressions which may evaluate arbitrary code hiding in the
copy-constructor's parameters.

Differential Revision: http://reviews.llvm.org/D8066

llvm-svn: 231328