The current GLIBC requirement of the nokogiri.so is version 2.17.
This means that distros before 2013 will be incompatible.

No need for libiconv on linux - it's part of glibc.

To updates to rake-compiler-dock-1.1.0, which does stripping of debug symbols per default.

It is not necessary to conditionally set cross_* options.
They are just ignored for native builds.
It is also wrong, since mingw availablility doesn't tell anything about cross builds for other platforms.

This also enables parallel builds for all 4 targets.
Run "rake gem:native -j1" to disable parallel builds.

They were not triggered due to the namespaced definition.

The generic "gem" task triggers the platform ruby gem in addition to each target.
Since the targets are started simultanously, this builds 4 times the same file.
That sometimes leads to build failures.
It can be avoided by generating only the specific target gem.

The previous task was also triggered in "rake compile" on the native platform.
Since the library dependencies are different then, compared to the cross build, it failed in this case.
Binding to a task that is only invoked in cross builds solves this issue.

It is the better choice in any case, since the new task is triggered at every cross build, even on re-runs.

and to fix build with current ruby-head.