x86-64, build: Always pass in -mno-sse

Always pass in the -mno-sse argument, regardless if
-preferred-stack-boundary is supported.  We never want to generate SSE
instructions in the kernel unless we *really* know what we're doing.

According to H. J. Lu, any version of gcc new enough that we support
it at all should handle the -mno-sse option, so just add it
unconditionally.

Reported-by: Kevin B. Smith <kevin.b.smith@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: H. J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/n/tip-j21wzqv790q834n7yc6g80j1@git.kernel.org
Cc: <stable@vger.kernel.org> # build fix only