Implement xsetbv(), xsave() and xrstor() providing C access to the similarly named CPU instructions.
Implement xsetbv(), xsave() and xrstor() providing C access to the
similarly named CPU instructions.

Since our in-tree binutils gas is not aware of the instructions, and
I have to use the byte-sequence to encode them, hardcode the r/m operand
as (%rdi). This way, first argument of the pseudo-function is already
placed into proper register.

MFC after:	1 week

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