hbm-minigbm: tweak bindgen match expression + capi helper renames
In build.rs, when invoking cbindgen::generate(), the resulting value of the match expression is unused, so tweak the match block such that it doesn't even produce a value.
Also rename the helpers in hbm-minigbm::capi to clarify whether they convert from/to C types, and whether they transfer ownership of heap pointers, or just const-borrow/mut-borrow.
Edited by Ryan Neph