Clarify license of shell scripts

[fredemmott]

The repo as a whole is marked as GPLv2, though the C and java files have an explicit header indicating they're GPL2, but the shell scripts don't.

Are the shell scripts also GPL2?

I'm looking at using these for another JIT (i.e. not using the JIT, just the dtrace + perf map stuff), and considering packaging an 'easy profiling' dev-dependency - but we'd want to use that with projects licensed under licenses such as MIT (e.g. https://github.com/hhvm/hhast/blob/master/LICENSE) or more obscure combinations such as PHP+Zend (e.g. https://github.com/facebook/hhvm/ - parts are taken from PHP itself so we can not use other licenses there)

If they are GPL, we'll likely document how to use them, but avoid distributing them or adding any dependencies on them.