C compiler from the Android NDK. For example,

	CGO_ENABLED=1 \
	GOOS=android \
	GOARCH=arm64 \
	CC_FOR_TARGET=$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android21-clang \
	./all.bash

To run tests on the Android device, add the bin directory to PATH so the
go tool can find the go_android_$GOARCH_exec wrapper generated by
make.bash. For example, to run the go1 benchmarks