First get the tooling:
$ sudo apt-get install gcc-arm-linux-gnueabihf
Then create another git checkout. I prefer the recently merged worktree support, since with that all your branches and remotes transparently work in the new checkout, too.
~/kernel/src/ $ git worktree add ../armhf HEAD
With that we're all set up. For building any
$branchwrap the following lines into a scrip:
$ cd ~/kernel/armhf
$ git checkout --detach $branch
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- multi_v7_defconfig zImage modules
I'm using --detach to avoid complaints from the git worktree code that I've checked out a branch already in the main repo. Note: Never accidentally run plain make in the ARM build directory - mixing up architectures seriously confuses the kernel build system.