Adding ARM building in Makefile

[elfgoh]

This PR enables an ARM binary to be build by running make release/goss-linux-arm. The resulting binary was ran on Beaglebone black debian and works fine when running

./goss-linux-arm  autoadd sshd
./goss-linux-arm validate

[elfgoh]

Addresses #272 and #211

[aelsabbahy]

What is the default value of GOARM when left blank?
https://github.com/golang/go/wiki/GoArm#supported-architectures

[aelsabbahy]

Also, need to add this new target as a dependency of build in the makefile. But otherwise looks good.

[elfgoh]

The default value is 6. Thought I have read a few sources stating that compiled ARMv6 binaries are backward compatible with v7 processors.

There are a few sources indicating that it is ideal to compile for ARMv6 as this will allow older RPI models to be supported. I recommend max compatibility using ARMv6

• https://www.alexruf.net/2016/01/16/cross-compile-with-go-1-5-for-raspberry-pi.html

You my have recognized that the optional variable GOARM has been set to 7. It enables support for ARMv7 instead of using the default value 6 for ARMv6. The difference is, that while the application will not run on old Raspberry Pi models, it takes advantage of a few more floating point registers and operations of the ARMv7 CPU from the Raspberry Pi 2. If you are in doubt, leave this variable unset for maximum compatibility unless you have a reason to adjust it.

• https://dave.cheney.net/2015/08/22/cross-compilation-with-go-1-5

Sure, knock yourself out, but that means your program won’t run on all models of the Raspberry Pi. The difference between GOARM=6 (the default) and GOARM=7 is enabling a few more floating point registers, and a few more operations that allow floating point double values to be passed to and from the ARMv7 (VPFv3) floating point co processor more efficiently. IMO, with the current Go 1.5 arm compiler, it’s not worth the bother.

[elfgoh]

Great! So I guess there will be ARM binaries in the next release?

[aelsabbahy]

Yup as of 3.5:

https://github.com/aelsabbahy/goss/releases/tag/v0.3.5

Wonder how many ARM users want to use goss :)

[elfgoh]

1 is a start :D