[build2] Generation of compilation databases on Linux

[Boris Kolpackov]

luizfernandoafrabrito at gmail.com <luizfernandoafrabrito at gmail.com> writes:

> I ended up using the following command to generate the compilation database:
> 
> $ b -v |& compiledb
> 
> where compiledb is a program that parses compilation commands.

That's actually a pretty good way to do it. We take care to print
accurate commands with -v with the idea that you should be able to
re-run them manually, etc.