zephyr/Makefile: Automatically derive target-specific CFLAGS.

By tricking Zephyt arch Makefiles compute them for us (not just for
Zephyr). This make potentially break as Zephyr evolves.

zephyr/Makefile

@@ -15,20 +15,18 @@ BOARD ?= qemu_x86
 # Zephyr 1.6.0
 OUTDIR_PREFIX = $(BOARD)
 
+# Zephyr (generated) config files - must be defined before include below
 Z_DOTCONFIG = outdir/$(OUTDIR_PREFIX)/.config
+Z_AUTOCONF_H = outdir/$(OUTDIR_PREFIX)/include/generated/autoconf.h
 DQUOTE = "
 # "
-include $(Z_DOTCONFIG)
-override ARCH = $(subst $(DQUOTE),,$(CONFIG_ARCH))
+include z_config_proxy.mk
 
 # Zephyr toolchain config is 2-pass, so included twice
 include $(ZEPHYR_BASE)/scripts/Makefile.toolchain.$(ZEPHYR_GCC_VARIANT)
 include $(ZEPHYR_BASE)/scripts/Makefile.toolchain.$(ZEPHYR_GCC_VARIANT)
 
-CFLAGS_arm = -mthumb -mcpu=cortex-m3 -mabi=aapcs
-CFLAGS_x86 = -fno-asynchronous-unwind-tables -ffreestanding -fno-stack-protector \
-    -fno-omit-frame-pointer -mpreferred-stack-boundary=2 -mno-sse -march=pentium
-CFLAGS_TARGET = $(CFLAGS_$(ARCH))
+CFLAGS_TARGET = $(cflags-y)
 
 include ../py/mkenv.mk
 include ../py/py.mk
@@ -64,8 +62,6 @@ KCONFIG_TARGETS = config nconfig menuconfig xconfig gconfig
 $(GENERIC_TARGETS) $(KCONFIG_TARGETS): $(LIBMICROPYTHON)
 	$(MAKE) -f Makefile.zephyr BOARD=$(BOARD) $@
 
-Z_AUTOCONF_H = outdir/$(OUTDIR_PREFIX)/include/generated/autoconf.h
-
 $(LIBMICROPYTHON): $(Z_AUTOCONF_H)
 build/genhdr/qstr.i.last: $(Z_AUTOCONF_H)
 
@@ -73,5 +69,12 @@ $(Z_AUTOCONF_H):
 	rm -f $(LIBMICROPYTHON)
 	-$(MAKE) -f Makefile.zephyr BOARD=$(BOARD)
 
+zephyr_arch.mk: $(Z_DOTCONFIG)
+	echo "include $(ZEPHYR_BASE)/arch/$(ARCH)/Makefile" >$@
+
+z_config_proxy.mk:
+	$(MAKE) -f Makefile.zephyr BOARD=$(BOARD) initconfig
+	echo "include z_config.mk" >$@
+
 # Clean Zephyr things too
-CLEAN_EXTRA = outdir
+CLEAN_EXTRA = outdir z_config_proxy.mk

zephyr/z_config.mk

+srctree = $(ZEPHYR_BASE)
+
+include $(Z_DOTCONFIG)
+override ARCH = $(subst $(DQUOTE),,$(CONFIG_ARCH))
+SOC_NAME = $(subst $(DQUOTE),,$(CONFIG_SOC))
+SOC_SERIES = $(subst $(DQUOTE),,$(CONFIG_SOC_SERIES))
+SOC_FAMILY = $(subst $(DQUOTE),,$(CONFIG_SOC_FAMILY))
+ifeq ($(SOC_SERIES),)
+SOC_PATH = $(SOC_NAME)
+else
+SOC_PATH = $(SOC_FAMILY)/$(SOC_SERIES)
+endif
+
+KBUILD_CFLAGS := -c
+include $(ZEPHYR_BASE)/scripts/Kbuild.include
+
+include $(ZEPHYR_BASE)/arch/$(ARCH)/Makefile