native/make/osx: circumvent unavailable gobjcopy

It's not used anyways, so just create an empty hex file if gobjcopy is
not found.
Merge pull request #2114 from LudwigOrtmann/native-osx-gobjcopy

native/make/osx: circumvent unavailable gobjcopy
travis: check PRs if they need squashing or depend on other PRs
Merge pull request #2090 from authmillenon/travis-squash-check

travis: squash check