[Issue 20204] need to fix ABI about registers using

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20204

--- Comment #1 from KnightMare <black80 at bk.ru> ---
I mean need to fix documentation and add some samples that shows which
registers will be used for it in Linux, Windows, _x64, ARM...

like Linux/x64 convention uses RDI, RSI, RDX, RCX, R8, R9 for args
left-to-right
but D uses same registers for args right-to-left:
extern (C) func( long a, long b, long c ) => C/Linux: RDI, RSI, RDX
extern (D) func( long a, long b, long c ) => C/Linux: RDX, RSI, RDI

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