package/environment-setup: add better kernel handling

Exporting ARCH and KERNELDIR makes easier to compile an external kernel
or out of tree kernel modules.

Signed-off-by: Angelo Compagnucci <angelo@amarulasolutions.com>
Reviewed-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/environment-setup/environment-setup

@@ -10,6 +10,7 @@ cat <<'EOF'
 Some tips:
 * PATH now contains the SDK utilities
 * Standard autotools variables (CC, LD, CFLAGS) are exported
+* Kernel compilation variables (ARCH, CROSS_COMPILE, KERNELDIR) are exported
 * To configure do "./configure $CONFIGURE_FLAGS" or use
   the "configure" alias
 * To build CMake-based projects, use the "cmake" alias

package/environment-setup/environment-setup.mk

@@ -11,6 +11,7 @@ define HOST_ENVIRONMENT_SETUP_INSTALL_CMDS
 	for var in $(TARGET_CONFIGURE_OPTS); do \
 		printf "export \"$$var\"\n" >> $(ENVIRONMENT_SETUP_FILE); \
 	done
+	printf "export \"ARCH=$(KERNEL_ARCH)\"\n" >> $(ENVIRONMENT_SETUP_FILE)
 	printf "export \"CROSS_COMPILE=$(TARGET_CROSS)\"\n" >> $(ENVIRONMENT_SETUP_FILE)
 	printf "export \"CONFIGURE_FLAGS=--target=$(GNU_TARGET_NAME) \
 		--host=$(GNU_TARGET_NAME) \
@@ -31,6 +32,10 @@ define HOST_ENVIRONMENT_SETUP_INSTALL_CMDS
 		$(ENVIRONMENT_SETUP_FILE)
 	printf "export \"PATH=\$$SDK_PATH/bin:\$$SDK_PATH/sbin:\$$PATH\"\n" \
 		>> $(ENVIRONMENT_SETUP_FILE)
+
+	$(if $(BR2_LINUX_KERNEL),\
+		printf "export \"KERNELDIR=$(LINUX_BUILDDIR)\"\n" \
+			>> $(ENVIRONMENT_SETUP_FILE),)
 endef
 
 $(eval $(host-generic-package))