RFR (S) 8208665: Amend cross-compilation docs with qemu-debootstrap recipe

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8208665

Webrev:
  http://cr.openjdk.java.net/~shade/8208665/webrev.02/

Not sure if building.html is supposed to be generated automatically?

This is the recipe I have been using for creating artifacts on my personal CI server [1], and it
seems to work reliably starting from jdk11. It is partially applicable for building jdk{8,9,10}, but
freetype and friends still need to be pointed out explicitly there. Nevertheless, this seems to be
the most straightforward way to cross-compile to foreign architectures if there are no devkit
bundles available.

Thanks,
-Aleksey

[1] https://builds.shipilev.net/