Support CRATE_TYPES argument for corrosion_import_crate

[vdimir]

Consider we have Cargo.toml with crate-type = ["staticlib", "cdylib"], but you need to build and use only one of them.
Editing of Cargo.toml is not an option (e.g., because it's in a third-party library).
Right now, you can't specify which type to use (adding a such option to corrosion_import_crate was my first thought).
But actually, you can set FLAGS --crate-type=staticlib, so *.so file won't be tried to build. Then, the only setback is copy_if_different still would try to copy the file. So, as suggested in this PR, we can probably operate only with files corresponding to the current BUILD_SHARED_LIBS settings.
Any feedback will be appreciated!

[jschwe]

Do you have a real-world usecase where the overhead of building the additional lib type is significant and a bottleneck?

[vdimir]

In my case, shared lib is failed to build (for some reason, it tries to link with gss_s even NO_STD is specified, but libgcc_s.so is not available in the toolchain, and it also quite difficult to edit). Most likely, it can be managed to build it, but the option to disable unrequited build looks more natural.

[jschwe]

The request itself is reasonable, however it would be a breaking change and it is quite likely that there are users relying on cdylibs always being built (thats also why the tests are failing here).

I'll have to think about if we can support this without breaking existing users.

[vdimir]

What do you think about the solution with introducing an option to corrosion_import_crate, like corrosion_import_crate(MANIFEST_PATH rust-lib/Cargo.toml CRATE_TYPE staticlib) ?

[jschwe]

What do you think about the solution with introducing an option to corrosion_import_crate, like corrosion_import_crate(MANIFEST_PATH rust-lib/Cargo.toml CRATE_TYPE staticlib) ?

I guess we could do that. Though I would suggest CRATE_TYPES instead and allow the user to specify multiple types (e.g. staticlib and bin ).

[jschwe]

Looks mostly good. I left some comments which should be addressed.
Also it would be good if you could add a description of the parameter to the Readme, and also note that the parameter currently only works with CMake >= 3.19.

[jschwe]

Looks good to me. Could you rebase and squash?