NCG: Don't double adjust SP before calls on Windows.

Windows ABI requires callers to allocate 32 byte of space in the parameter stack space. This should be rolled into the stack adjustment for

Currently we generate this code:

	subq $8,%rsp   # for stack alignment?
	movq %r13,%rcx # Arg1
	movq %rbx,%rdx # Arg2
	subq $32,%rsp  # Reserve "shadow" space + align stack if required
	xorl %eax,%eax # Not required for windows, even on linux only for vararg functions
	call newCAF

	addq $40,%rsp
	testq %rax,%rax
	je _c9N5

Ideally this should become

	movq %r13,%rcx # Arg1
	movq %rbx,%rdx # Arg2
	subq $40,%rsp  # Reserve "shadow" space
	xorl %eax,%eax
	call newCAF

	addq $40,%rsp
	testq %rax,%rax
	je _c9N5

I haven't looked deeper into this and don't plan in the near future.

But if anyone is interested I'm willing to lend a hand.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Task
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler (CodeGen)
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