noux: handle missing shared object gracefully

[cnuke]

Executing a binary in noux w/o having all shared objects already in place
results in abort():

[init -> noux] replay: missing ds_info for dataspace at addr 0x11000
unmapping of managed dataspaces not yet supported
unmapping of managed dataspaces not yet supported
[init -> noux] Could not open file "pcre.lib.so"
[init -> noux] C++ runtime: Genode::Rom_connection::Rom_connection_failed
[init -> noux] void* abort(): abort called

It would be better to notify the user instead, imho.

[alex-ab]

@chelmuth: may you please add 1fcf45c to staging, the other part of the issue commit "add missing .so files to noux_tool_chain.inc" is already on master

[chelmuth]

Sorry, the commit just slipped through :-|