tcg/i386: Add support for w64 ABI

w64 uses the registers rcx, rdx, r8 and r9 for function arguments,
so it needs a different declaration of tcg_target_call_iarg_regs.

rax, rcx, rdx, r8, r9, r10 and r11 may be changed by function calls.

rbx, rbp, rdi, rsi, r12, r13, r14 and r15 remain unchanged by function calls.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Stefan Weil <sw@weilnetz.de>