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

arch/x86/Makefile

@@ -31,6 +31,9 @@ ifeq ($(CONFIG_X86_32),y)
 
         KBUILD_CFLAGS += -msoft-float -mregparm=3 -freg-struct-return
 
+        # Don't autogenerate SSE instructions
+	KBUILD_CFLAGS += -mno-sse
+
         # Never want PIC in a 32-bit kernel, prevent breakage with GCC built
         # with nonstandard options
         KBUILD_CFLAGS += -fno-pic
@@ -57,8 +60,11 @@ else
         KBUILD_AFLAGS += -m64
         KBUILD_CFLAGS += -m64
 
+        # Don't autogenerate SSE instructions
+	KBUILD_CFLAGS += -mno-sse
+
 	# Use -mpreferred-stack-boundary=3 if supported.
-	KBUILD_CFLAGS += $(call cc-option,-mno-sse -mpreferred-stack-boundary=3)
+	KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3)
 
         # FIXME - should be integrated in Makefile.cpu (Makefile_32.cpu)
         cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)