kernel: add compile fix for linux 4.9 on x86

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/patches-4.9/011-kbuild-export-SUBARCH.patch

+--- a/Makefile
++++ b/Makefile
+@@ -414,8 +414,8 @@ KERNELRELEASE = $(shell cat include/conf
+ KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
+ 
+ export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
+-export ARCH SRCARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
+-export CPP AR NM STRIP OBJCOPY OBJDUMP
++export ARCH SRCARCH SUBARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD
++export CC CPP AR NM STRIP OBJCOPY OBJDUMP
+ export MAKE AWK GENKSYMS INSTALLKERNEL PERL PYTHON UTS_MACHINE
+ export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
+