Adding a build stage for arm64 cni

[pjohnst5]

Reason for Change:
We need to build an ARM64 version of CNI too now.
Validation on an ARM64 machine:

azureuser@test-vm:~$ lscpu
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              32
On-line CPU(s) list: 0-31
Thread(s) per core:  1
Core(s) per socket:  32
Socket(s):           1
NUMA node(s):        1
Vendor ID:           Cavium
Model:               2
Model name:          ThunderX2 99xx
Stepping:            0x1
BogoMIPS:            400.00
NUMA node0 CPU(s):   0-31
Flags:               fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm
azureuser@test-vm:~$ sudo ./azure-vnet
v1.4.11

And when I try running an amd64`cni binary on an arm64 machine, it fails

azureuser@test-vm:~$ sudo amd64/azure-vnet
amd64/azure-vnet: 3: amd64/azure-vnet: Syntax error: end of file unexpected (expecting ")")

[rbtr]

rather than new build steps, could the existing build steps be updated to take a matrix of build args? it seems unlikely that this is the last GOOS or GOARCH change we will ever have to make, and that would:

• reduce the existing build stages since we don't really need separate steps for different GOOS/GOARCH
• give us a head start on having arm64 builds for all the rest of our components.

[pjohnst5]

Hi Evan, what would that look like? I like the idea, just don't really know what it would look like

[rbtr]

I think this could be as easy as adding a make target to the effect of make all-binaries-multiplatform that takes arrays of GOOS and GOARCH values, something like

make all-binaries-multiplatform GOOSES=linux,windows GOARCHES=arm64,amd64

then that make target could iterate those arrays to build the matrix of build targets, and just call the existing make targets with update build args:

all-binaries-multiplatform:
	for goos in $(GOOSES):
		for goarch in $(GOARCHES):
			$(MAKE) all-binaries GOOS=$$goos GOARCH=$$goarch

but...in actual shell script😁

[rbtr]

blocking on discussed multiplatform change

[pjohnst5]

Trying out the for loop way, where we pass in GOOS=linux,windows GOARCH=amd64,arm64

[rbtr]

multiplat target looks good 💯 just a couple cleanup things around it

[rbtr]

lgtm