Require `make` is run before `make install`

I can't quite remember why this ifdef is present to silently run `make` as a
normal user, and it doesn't seem to work if `make install` is run while as root,
so I'm just removing it and requiring that `make` is run before `make install`
unconditionally.

Closes #708
auto merge of #711 : alexcrichton/cargo/issue-708, r=brson

I can't quite remember why this ifdef is present to silently run `make` as a
normal user, and it doesn't seem to work if `make install` is run while as root,
so I'm just removing it and requiring that `make` is run before `make install`
unconditionally.

Closes #708