Fix compilation of x86emu with gcc 4.6.x

Fix compilation of x86emu with gcc 4.6.x

gcc 4.6 complains about unused but set variables in x86emu.
Particularly some variables are always set but only used in
debug mode, or when FPU support is enabled.

Change-Id: Ic53bd2303171ab717eb2d2c0ed72744d3eb6989e
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/258
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>