add support for released packages

[pseyfert]

ATM only nightly builds of LHCb software are supported. released versions would also be nice.

[pseyfert]

the compile_commands.json do not point to any specific version of upstream projects for current builds. they just use whatever is currently on the build server (which makes sense at the time of building the release). as it looks, parsing the cmake files is necessary.

In old releases, the build server used a versioned subdirectory.