With this patch, the thread context area RM session gets created at
program startup to have the thread context area's virtual address range
reserved right from the beginning.
Fixes#734.
This patch implies that all Genode processes try to create an RM
session. So a route to the RM service must be present even for processes
that have only a single thread. Hence, the patch contains an update of
affected components.
The new 'genode_envp' variable declared in '_main.cc' allows libc
plugins to supplying custom environment pointers to the main function.
This is needed by 3rd-party software such as GNU make, which expects the
environment pointer as third argument of the main function.