This change rewrites `out` and `inout` parameters to be implemented on
the AST. The parameter copying behavior is modeled on the AST and
generated through codegen.

Instead of using the previously existing infrastructure for generating
HLSL's copy-in/copy-out semantaics, this change generates temporaries
based on the AST, uses AST-based analysis for optimziation, and uses
the Objective-C indirect writeback support for copy-out.

'cbieneman/rewrite-out-params' on '617b5097828'.

'cbieneman/rewrite-out-params' on '617b5097828'.

'cbieneman/rewrite-out-params' on '617b5097828'.

'cbieneman/rewrite-out-params' on '617b5097828'.

'cbieneman/rewrite-out-params' on '4cf0f6c6504'.

I need to clean up the lvalue bindings in CGF, but otherwise this is
going in the right direction.

SrcLV is Base with its casts stripped, but we only initialize it if we
have a writeback cast sequence, otherwise we can just use Base.

This handles SrcLV for non-simple values where the address might not be
available.

This change simplifies the casting chain for HLSL C-style casts that
are either derived to base conversions or casting an object to itself.
In both cases HLSL defines returning lvalues.

This change collapses the cast chains down. Before this change all the
CStyleCastExprs were genreated as `NoOp` casts with `ImplicitCastExpr`
cast chains leading up to them.

tools/clang/test/HLSLFileCheck/hlsl/classes/derived-to-base-casting.hlsl

This should all be done at the AST level

Under the MSVC ABI arguments are emitted right to left, but writebacks
need to be emitted left to right for HLSL.

This is probably a case that we need to look into more.

If we have an unsized array we can't generate a temporary for it. That
makes unsized arrays as function parameters an odd special case that we
should fix.

This reverts commit 93635eb.

The old test verified incorrect debug info based on incorrect code
generation. This test verifies correct debug info.

../tools/clang/test/HLSLFileCheck/dxil/debug/out_args.hlsl

This reverts commit 3307009.

../lib/Transforms/Scalar/ScalarReplAggregatesHLSL.cpp