[build2] bpkg and bdep licensing

[Boris Kolpackov]

Matthew Krupcale <mkrupcale at matthewkrupcale.com> writes:

> Given that both pieces of software (build2 and ODB) are copyright Code
> Synthesis, is there a linking exception being employed so that bpkg and
> bdep can remain licensed as MIT?

Yes, we give ODB license exceptions to open source projects that use
incompatible licenses[1]. And so it was implied that build2 will go
the same route. But I guess now is good time to formalize this:

https://git.codesynthesis.com/cgit/odb/odb-etc/tree/license-exceptions/build2-odb-license-exception.txt

I've also added notes to the LICENSE files in bpkg and bdep.

[1] https://www.codesynthesis.com/~boris/blog/2012/08/22/odb-license-exception/