AndroidKernel: add support to pass build flags

Add support to pass build flags while compiling Linux kernel.

This change is required to add support in Linux kernel to use external
host executable. (example: dtc)

Usage example:
TARGET_KERNEL_MAKE_ENV := DTC_EXT=dtc$(HOST_EXECUTABLE_SUFFIX)

Change-Id: I008ca00cf9695133ff167ffdee8d8dfb89beb598
Signed-off-by: Shashank Mittal <mittals@codeaurora.org>
Signed-off-by: Puja Gupta <pujag@codeaurora.org>
diff --git a/AndroidKernel.mk b/AndroidKernel.mk
index d28f7ba..b5f7dac 100644
--- a/AndroidKernel.mk
+++ b/AndroidKernel.mk
@@ -6,6 +6,13 @@
 INSTALLED_KERNEL_TARGET := $(PRODUCT_OUT)/kernel
 endif
 
+TARGET_KERNEL_MAKE_ENV := $(strip $(TARGET_KERNEL_MAKE_ENV))
+ifeq ($(TARGET_KERNEL_MAKE_ENV),)
+KERNEL_MAKE_ENV :=
+else
+KERNEL_MAKE_ENV := $(TARGET_KERNEL_MAKE_ENV)
+endif
+
 TARGET_KERNEL_ARCH := $(strip $(TARGET_KERNEL_ARCH))
 ifeq ($(TARGET_KERNEL_ARCH),)
 KERNEL_ARCH := arm
@@ -121,26 +128,26 @@
 	mkdir -p $(KERNEL_OUT)
 
 $(KERNEL_CONFIG): $(KERNEL_OUT)
-	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG)
+	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG)
 	$(hide) if [ ! -z "$(KERNEL_CONFIG_OVERRIDE)" ]; then \
 			echo "Overriding kernel config with '$(KERNEL_CONFIG_OVERRIDE)'"; \
 			echo $(KERNEL_CONFIG_OVERRIDE) >> $(KERNEL_OUT)/.config; \
-			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fi
+			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fi
 
 $(TARGET_PREBUILT_INT_KERNEL): $(KERNEL_OUT) $(KERNEL_HEADERS_INSTALL)
 	$(hide) echo "Building kernel..."
 	$(hide) rm -rf $(KERNEL_OUT)/arch/$(KERNEL_ARCH)/boot/dts
-	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS)
-	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS) modules
-	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) INSTALL_MOD_PATH=$(BUILD_ROOT_LOC)../$(KERNEL_MODULES_INSTALL) INSTALL_MOD_STRIP=1 ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) modules_install
+	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS)
+	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_CFLAGS) modules
+	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) INSTALL_MOD_PATH=$(BUILD_ROOT_LOC)../$(KERNEL_MODULES_INSTALL) INSTALL_MOD_STRIP=1 $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) modules_install
 	$(mv-modules)
 	$(clean-module-folder)
 
 $(KERNEL_HEADERS_INSTALL): $(KERNEL_OUT)
 	$(hide) if [ ! -z "$(KERNEL_HEADER_DEFCONFIG)" ]; then \
 			rm -f $(BUILD_ROOT_LOC)$(KERNEL_CONFIG); \
-			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_HEADER_DEFCONFIG); \
-			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) headers_install;\
+			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_HEADER_DEFCONFIG); \
+			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_HEADER_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) headers_install;\
 			if [ -d "$(KERNEL_HEADERS_INSTALL)/include/bringup_headers" ]; then \
 				cp -Rf  $(KERNEL_HEADERS_INSTALL)/include/bringup_headers/* $(KERNEL_HEADERS_INSTALL)/include/ ;\
 			fi ;\
@@ -148,20 +155,20 @@
 	$(hide) if [ "$(KERNEL_HEADER_DEFCONFIG)" != "$(KERNEL_DEFCONFIG)" ]; then \
 			echo "Used a different defconfig for header generation"; \
 			rm -f $(BUILD_ROOT_LOC)$(KERNEL_CONFIG); \
-			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG); fi
+			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) $(KERNEL_DEFCONFIG); fi
 	$(hide) if [ ! -z "$(KERNEL_CONFIG_OVERRIDE)" ]; then \
 			echo "Overriding kernel config with '$(KERNEL_CONFIG_OVERRIDE)'"; \
 			echo $(KERNEL_CONFIG_OVERRIDE) >> $(KERNEL_OUT)/.config; \
-			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fi
+			$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) oldconfig; fi
 
 kerneltags: $(KERNEL_OUT) $(KERNEL_CONFIG)
-	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) tags
+	$(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) tags
 
 kernelconfig: $(KERNEL_OUT) $(KERNEL_CONFIG)
 	env KCONFIG_NOTIMESTAMP=true \
-	     $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) menuconfig
+	     $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) menuconfig
 	env KCONFIG_NOTIMESTAMP=true \
-	     $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) savedefconfig
+	     $(MAKE) -C $(TARGET_KERNEL_SOURCE) O=$(BUILD_ROOT_LOC)$(KERNEL_OUT) $(KERNEL_MAKE_ENV) ARCH=$(KERNEL_ARCH) CROSS_COMPILE=$(KERNEL_CROSS_COMPILE) savedefconfig
 	cp $(KERNEL_OUT)/defconfig $(TARGET_KERNEL_SOURCE)/arch/$(KERNEL_ARCH)/configs/$(KERNEL_DEFCONFIG)
 
 endif