Make examples be compiled correctly

Why is the command only printed?
I found this very confusing because it seems like the examples were built correctly,
while actually nothing happened.

Note that I removed the -Llib flag because that caused the compiler to crash if you have installed the library because of [this issue](https://github.com/mozilla/rust/issues/11195).
Currently, getting the examples to work is a bit of a pain:

Prerequisites:
- Do not install rustc in /usr/local/lib/
- Change the RUSTC variable to the path to your rustc binary
- Make sure to have installed glfw-rs

Commands:
- make
- sudo make install
- make examples