build fails on Mac with MacPorts, because of libgit2

[RJVB]

The libgit2-sys package is written to use iconv on Mac, but assumes only the system version is available. When using MacPorts there will also an up-to-date libiconv installed which causes a build failure:

:info:build   = note: Undefined symbols for architecture x86_64:
:info:build             "_iconv", referenced from:
:info:build                 _git_fs_path_iconv in liblibgit2_sys-0e14e63160044187.rlib(fs_path.o)
:info:build                (maybe you meant: _git_fs_path_iconv_init_precompose, _git_fs_path_iconv , _git_fs_path_iconv_clear )
:info:build             "_iconv_open", referenced from:
:info:build                 _git_fs_path_direach in liblibgit2_sys-0e14e63160044187.rlib(fs_path.o)
:info:build             "_iconv_close", referenced from:
:info:build                 _git_fs_path_direach in liblibgit2_sys-0e14e63160044187.rlib(fs_path.o)
:info:build           ld: symbol(s) not found for architecture x86_64
:info:build           clang: error: linker command failed with exit code 1 (use -v to see invocation)
:info:build
:info:build error: could not compile `cargo-cache` due to previous error

I am not that interested in the git gc functionality, which is too costly for the potential gain it can give. Maybe it's possible to make this an optional feature?

[triscuitcircuit]

Same issue here