Rename the OpenAL target if also building the router

Rename the OpenAL target if also building the router

This is rather ugly, but it's necessary to get a proper export configuration.
The issue was that the main OpenAL target library name is set to soft_oal when
the router is being built, which is incorrect for the exported config library.
Exporting the router would have the incorrect name of OpenAL::Router.

So this change has the router use the OpenAL target name when it's built, which
is good since it will have the standard OpenAL lib name for apps to link to and
get the OpenAL::OpenAL export name. The main library's target name is changed
in this case to avoid conflicts.