Makefile does not support `DEBUG=1` anymore...

[janjongboom]

As far as I can see - using the local export to makefile - make DEBUG=1 no longer produces a debug build.

I fixed it this way by patching the Makefile, but I'm unsure how to translate this patch into a proper PR against the Makefile exporter.

@theotherjimmy @sg- @bridadan

[bridadan]

I think it will work if you do mbed export --profile debug?

[janjongboom]

@bridadan \o/ ! Yeah that works.