pthread_main_np not implemented

[Steven Harp]

After upgrading to 17.11, I noticed some of my libc+lwip using programs have
started logging many warnings like:

   pthread_main_np_int: pthread_main_np called, not implemented

This is observed with a fresh checkout (under x86_32/nova); so,
I presume the cause is distinct from the similar warnings noted in #2312.

Possibly related (?), during build, there were also quite a few warnings
like:

 libports/src/lib/libc_lwip/plugin.cc:284:31: 
   warning: ‘Genode::Env_deprecated* Genode::env()’ is deprecated [-Wdeprecated-declarations]
  Genode::destroy(Genode::env()->heap(), context(fdo));

The programs actually seem to work, but the logs are "overly colorful".

Perhaps there is some initialization that needs to be done differently?
Any diagnostic hints appreciated.

// Steve Harp