[ARM64] [Windows] Follow MS X86_64 C++ ABI when passing structs

[ARM64] [Windows] Follow MS X86_64 C++ ABI when passing structs

Summary: Microsoft's C++ object model for ARM64 is the same as that for X86_64.
For example, small structs with non-trivial copy constructors or virtual
function tables are passed indirectly.  Currently, they are passed in registers
when compiled with clang.

Reviewers: rnk, mstorsjo, TomTan, haripul, javed.absar

Reviewed By: rnk, mstorsjo

Subscribers: kristof.beyls, chrib, llvm-commits, cfe-commits

Differential Revision: https://reviews.llvm.org/D49770

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@338076 91177308-0d34-0410-b5e6-96231b3b80d8