No arm-linux-androideabi-gcc in prebuilts for ndk r21d

Hi I'm trying to build a custom android kernel.

I was told to $ export CROSS_COMPILE=/home/user/adb-fastboot/kernel-custom/android-ndk-r21d/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi- with nothing after the dash

But when I $ make clean && make mrproper I get

make: /home/user/adb-fastboot/kernel-custom/android-ndk-r21d/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc: Command not found

So when I assume that make clean isn't mandatory and do $ make -j8 I also get

make: /home/user/adb-fastboot/kernel-custom/android-ndk-r21d/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc: Command not found

I just downloaded the ndk from there and clicked "ectract here" on a linux machine https://developer.android.com/ndk/downloads but I can't find any arm-linux-androideabi-gcc file anywhere in the extracted folder...

What should I do to manage to compile please?

Regards