[feature request] support GHDL as source for .vhdl files

[werdahias]

In Debian, ghdl-common provides almost all files that are present under vhdl_libraries. In general, vendoring code is frowned upon in Debian, and since the files present are identical, I would prefer it if this ghdl-common was natively supported as drop-in.
According to https://ghdl.github.io/ghdl/using/ImplementationOfVITAL.html vital2000 is not yet supported; if the ieee2008, std and synopsys parts could be sourced form ghdl-common this would help a lot.

I can provide a MR is this is something you agree on

[Schottkyc137]

In theory I an approve of this, but I'm not quite sure what exactly you mean by the native support. Do you mean something like adding ghdl-common as a "submodule" to rust_hdl?

[werdahias]

yes. Ideally, vhdl_ls looks for the vhdl files from GHDL-common, and then uses vhdl_libraries as fallback. This would greatly ease packaging vhdl_ls for Debian