[COFF][ARM64] Reorder handling of aarch64 MSVC builtins

In `CodeGenFunction::EmitAArch64BuiltinExpr()`, bulk move all of the aarch64 MSVC-builtin cases to an earlier point in the function (the `// Handle non-overloaded intrinsics first` switch block) in order to avoid an unreachable in `GetNeonType()`. The NEON type-overloading logic is not appropriate for the Windows builtins.

Fixes https://llvm.org/pr42775

Differential Revision: https://reviews.llvm.org/D65403

llvm-svn: 367323