CoreDSL2 Frontend: Support custom include search paths via -Ipath/to/cdsl/files

[PhilippvK]

I have to use include statements like ../rv_base/RVI.core_desc at several places which is problematic if the base coredsl files is located somewhere als and the code should be useable in multiple different projects (with other directory structures).

I would like to replace the includes by just RVI.core_desc and allow users to specify any number of possible include paths (of course . will be the default and the syntax/behavior should be consistent with GCC)

Are there any objections to this? I am unsure if this should be discussed with the CoreDSL spec and eventually be added to the Specification. On the one hand this is just tool-specific, but of course we do not want to break other 3rd party tooling with these changes…