mmap implementation for ANON mapping with desired address

[Alexander Tormasov]

Hello Norman,
I make once again attempt to implement the mmap with MAP_FIXED|MAP_ANON
Now I think that it is closer to what I need for golang runtime, at least it works here.
Could you take a look?

Due to specific of my tests it appears in 2 patches to genode master (Oct 23 2020):
https://github.com/tor-m6/genode/commit/0aa7bb95ce451dc99d2cb76b1a4da09d64783a98
and 2 files (repos/libports/lib/symbols/libc and repos/ports/src/noux-pkg/go_app/anon_mmap.cc with main algorithm) from here
https://github.com/tor-m6/genode/commit/0248ae78851833cfef64068e99764f4fddd2294b

(sorry, still have some whitespaces and code style changes in patches)

Question: is it worth to spend more efforts to bring it to the mainstream genode?
or continue keeping them in the private repository as now?

Same question for golang support…
It can be potentially stored in world repo - is it worth to spend efforts?
May be someone interested to takeover this work?

Sincerely,
Alexander