devel/cargo-c: update to 0.10.15

NOTE: Whenever we can import this or, a newer version, the patches in
devel/cargo-c should be applied again. These are not needed on amd64
so, for now I'm not going to bother as these may change before the import.

v0.10.5
Fixes

 - Fix non-POSIX paths in Libdir under Windows by @amyspark
 - Fix static_libraries swallowing sequence of -framework flags by @amyspark
 - Rust integration tests now can link and run fine by @lu-zero

New features

 - Allow disabling emission of library version constants in header files by @sd-collins

Version Bumps

 - implib 0.4.0
 - cargo 0.90
