Makefile: Use -fno-tree-vectorize on x86-64

This patch adds '-fno-tree-vectorize' to x86-64 GCC options to fix test
breakage caused by commit 034ac4b ("Makefile: Use GCC '-O3' optimization
level").

Suggested-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

Makefile

@@ -194,6 +194,9 @@ WARNINGS	+=				\
 DEFAULT_CFLAGS	+= $(WARNINGS)
 
 OPTIMIZATIONS	+= -O3 -fno-delete-null-pointer-checks
+ifeq ($(uname_M),x86_64)
+OPTIMIZATIONS	+= -fno-tree-vectorize
+endif
 DEFAULT_CFLAGS	+= $(OPTIMIZATIONS)
 
 INCLUDES	= -Iinclude -Iarch/$(ARCH)/include -Isys/$(SYS)-$(ARCH)/include -Ijit -Ijit/glib -include $(ARCH_CONFIG) -Iboehmgc/include