sclang: handle signals (SIGTERM)

[sjomae]

On Linux, when running sclang from the command line, a Ctrl+c stops both sclang and scsynth.

When sending SIGTERM, SIGINT or SIGHUP to sclang only sclang is terminated and scsynth is still running, which is probably the right thing to do.

(Why does it act different on Ctrl+c, isn't that sending SIGINT?)

Would it be possible to let the user of sclang define a function / method which handles signals? So a custom signal handler for if sclang receives SIGTERM for instance. Then the user can decide to send \quit to scsynth, for instance, when receiving SIGTERM.

Some languages use the following signal mapping for Windows:
CONTROL_C_EVENT and CTRL_BREAK_EVENT is mapped to SIGINT
CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT and CTRL_SHUTDOWN_EVENT is mapped to SIGTERM.
https://pkg.go.dev/os/signal#hdr-Windows