Don't copy objects with trivial, deleted copy ctors

This affects both the Itanium and Microsoft C++ ABIs.

This is in anticipation of a change to the Itanium C++ ABI, and should
match GCC's current behavior.  The new text will likely be:

"""
Pass an object of class type by value if every copy constructor and
move constructor is deleted or trivial and at least one of them is not
deleted, and the destructor is trivial.
"""
http://sourcerytools.com/pipermail/cxx-abi-dev/2014-May/002728.html

On x86 Windows, we can mostly use the same logic, where we use inalloca
instead of passing by address.  However, on Win64, there are register
parameters, and we have to do what MSVC does.  MSVC ignores the presence
of non-trivial move constructors and only considers the presence of
non-trivial or deleted copy constructors.  If a non-trivial or deleted
copy ctor is present, it passes the argument indirectly.

This change fixes bugs and makes us more ABI compatible with both GCC
and MSVC.

Fixes PR19668.

Reviewers: rsmith

Differential Revision: http://reviews.llvm.org/D3660

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208786 91177308-0d34-0410-b5e6-96231b3b80d8
clang-cl: Fall back immediately if /GR and /fallback were both passed

None of our tests use /fallback, so this lets us gradually add RTTI
support without breaking projects using /fallback.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208787 91177308-0d34-0410-b5e6-96231b3b80d8