Use -mno-sse to prevent overzealous gcc optimizations

Use -mno-sse to prevent overzealous gcc optimizations

The offending part that made coreboot crash with some toolchains
was that gcc emits SSE instructions but coreboot did not enable SSE at
that point.

Since the gain for coreboot using SSE instructions is not measurable,
let's not use SSE instructions rather than enabling SSE early on.
One rationale behind this is that other parts of coreboot, like the
SMM handler would need fixing because the XMM registers are not saved
on SMM entry. Thus keep it simple.

Change-Id: I14f0942f300085767ece44cec570fb15c761e88d
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/694
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>