Update `macvim` package to v7.4.355

MacVim's maintenance has stagnated, so this moves `macvim` to a new maintainer.
Additionally, the `-headerpad_max_install_names` linker flag is passed to
prevent problems when setting the rpaths.
Merge pull request #3201 from cstrahan/update-macvim

Update `macvim` package to v7.4.355