runtime: save get_exename(), so we are more safe in fatal_exit
* fatal_exit dumps backtrace also on macosx
* fatal_exit shows better explanation of signal
* posix/initialize_platform_runtime: install also SIGILL
* posix/get_debug_info: use addr2line only on linux
* posix/get_debug_info: use dladdr when available (macosx,linux, configured in autoconf)
get_debug_info fix type for linux