Add a 'GenodeEnv' type and a 'componentConstructHook' to the system
module. The 'componentConstructHook' allows for detection of POSIX style
programs that exit implicitly or native Genode components that
initialize to serve RPC requests and OS signals.
This hook takes a 'GenodeEnv' argument so that the environment interface
is passed cleanly to application code after globals are initialized.
This is an typed pointer to a C++ object, procedures for accessing the
environment will be available from a Nimble library and not included in
the standard library.
The standard library has an internal pointer to the environment object
but this is not for external use, the undocumented global environment
pointer has been removed.
