[clang codegen] Fix ABI for HVA returns on AArch64 MSVC.

MSVC normally has a bunch of restrictions on returning values directly
which don't apply to passing values directly.  (This roughly corresponds
to the definition of a C++14 aggregate.)  However, these restrictions
don't apply to HVAs; make sure we check for that.

Fixes https://github.com/llvm/llvm-project/issues/62223

Differential Revision: https://reviews.llvm.org/D153179