Samsung decided (for some reason) that it was a good idea to hardcode the cross-compiler. This does not play nice with any sane build system, so I patched it.
--- a/Makefile
+++ b/Makefile
@@ -198,7 +198,7 @@ SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
 #ARCH		?= $(SUBARCH)
 #CROSS_COMPILE	?= $(CONFIG_CROSS_COMPILE:"%"=%)
 ARCH		?= arm64
-CROSS_COMPILE= ../PLATFORM/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.8/bin/aarch64-linux-android-
+CROSS_COMPILE ?= ../PLATFORM/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.8/bin/aarch64-linux-android-
 
 # Architecture as present in compile.h
 UTS_MACHINE 	:= $(ARCH)