x86: Explicitly disable sse

Previously the external build system was relied upon for disablingdisabling sse.
This is not desirable as it has the affect of disabling sse for the entire user
level build. Instead, since we only want to disable it for the kernel, we will
disable it here in the kernel Makefile

Makefile

@@ -348,7 +348,7 @@ endif
 endif # SEL4_ARCH=aarch32
 endif # ARCH=arm
 ifeq (${ARCH}, x86)
-CFLAGS += -m32 -mno-mmx -mno-sse
+CFLAGS += -m32
 ASFLAGS += -Wa,--32
 DEFINES += -DARCH_IA32 -DARCH_X86 -DX86_32 -D__KERNEL_32__
 LDFLAGS += -Wl,-m,elf_i386 
@@ -415,6 +415,13 @@ ifeq (${CONFIG_WHOLE_PROGRAM_OPTIMISATIONS_KERNEL}, y)
     CFLAGS += -fwhole-program
 endif
 
+# Set kernel build specific flags for the different x86 variants
+# These are set here and not by the common build system as they
+# only apply to building the kernel, and nothing else
+ifeq (${ARCH}, x86)
+CFLAGS += -mno-mmx -mno-sse -mno-sse2 -mno-3dnow
+endif
+
 # Allow overriding of the CFLAGS. Use with caution.
 ifdef CONFIG_KERNEL_CFLAGS
 ifneq (${CONFIG_KERNEL_CFLAGS},)