Use core c_void type and remove need for libc

[GuillaumeGomez]

It created an issue in sysinfo.

[GuillaumeGomez]

Oh, that requires to upgrade the minimum supported rust version...

@retep998: Should I automatically detect the version of the rustc compiler like libc does to enable it through a feature maybe?

[retep998]

This change will be done in 0.4 when the MSRV is bumped