Make build path absolute in whole context

[facchinm]

Test PR for #235

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/arduino-builder/arduino-builder-308.zip

ℹ️ To test this build:

1. Replace arduino-builder binary (you can find it where you installed the IDE) with the provided one

[matthijskooijman]

I had a look at this, I found that the core build path (and thus the core archive path) is made absolute here: https://github.com/arduino/arduino-builder/blob/master/add_additional_entries_to_context.go#L44

If the buildpath would be made absolute earlier, than all these filepath.Abs() could be removed, I guess.

If the path is made absolute, this is probably the best place: https://github.com/arduino/arduino-builder/blob/master/arduino-builder/main.go#L314

If no explicit build path is generated, an automatic one is generated which is probably already absolute: https://github.com/arduino/arduino-builder/blob/master/generate_buildpath_if_missing.go
https://github.com/arduino/arduino-builder/blob/master/generate_buildpath_if_missing.go

[facchinm]

Agree with going back to the source

arduino-builder/arduino-builder/main.go

Line 314 in bbf7051

ctx.BuildPath = buildPath

🙂 Will modify the PR in a bit-

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/arduino-builder/arduino-builder-308.zip

ℹ️ To test this build:

1. Replace arduino-builder binary (you can find it where you installed the IDE) with the provided one