Allow --cpu= to work for x86.
Allow --cpu= to work for x86.

--cpu was already implemented for most of our embedded
platforms, this just extends it to x86.  Corner case for
Atom processor as it doesn't respond to the --march=
option under icc.

Change-Id: I2d57a7a6e9d0b55c0059e9bc46cfc9bf9468c185

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