toolchain/toolchain-external: error if BR2_TOOLCHAIN_EXTERNAL_PATH is not set

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
[Arnout: add BR_BUILDING condition]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 8e91385a2cb81c5f8114354f4494230e2aebb93a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

toolchain/toolchain-external/pkg-toolchain-external.mk

@@ -69,7 +69,12 @@ ifeq ($(BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD),y)
 TOOLCHAIN_EXTERNAL_INSTALL_DIR = $(TOOLCHAIN_EXTERNAL_DOWNLOAD_INSTALL_DIR)
 else
 TOOLCHAIN_EXTERNAL_INSTALL_DIR = $(abspath $(call qstrip,$(BR2_TOOLCHAIN_EXTERNAL_PATH)))
+ifeq ($(BR2_TOOLCHAIN_EXTERNAL)$(BR_BUILDING),yy)
+ifeq ($(TOOLCHAIN_EXTERNAL_INSTALL_DIR),)
+$(error No external toolchain path set, check your BR2_TOOLCHAIN_EXTERNAL_PATH setting)
+endif
 endif
+endif # BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD
 
 ifeq ($(TOOLCHAIN_EXTERNAL_INSTALL_DIR),)
 ifneq ($(TOOLCHAIN_EXTERNAL_PREFIX),)