Set Ctrl-C signal handler

[certik]

This allows to catch Ctrl-C from within a running command, but unfortunately still exits. Also there seems to be some thread (?) still running in the background, since I get some later error message while I am already back in Bash:

~/repos/shell(ctrl_c2)$ cat
^CReceived Ctrl+C

~/repos/shell(ctrl_c2)$ cat: Input/output error (os error 5)
Error: Errno(EIO)

~/repos/shell(ctrl_c2)$

[certik]

On Windows on the other hand it does not exit the shell:

~/repos/shell(ctrl_c2)$ ../lfortran/src/bin/lfortran
Interactive Fortran. Experimental prototype, not ready for end users.
LFortran version: 0.40.0-57-gb50db1203
  * Use Ctrl-D to exit
  * Use Enter to submit
  * Use Alt-Enter or Ctrl-N to make a new line
    - Editing (Keys: Left, Right, Home, End, Backspace, Delete)
    - History (Keys: Up, Down)
>>> Received Ctrl+C                                                           1,1   ]
~/repos/shell(ctrl_c2)$

Although it leaves the terminal in a bad state (up arrow prints [A instead of showing the previous command), but that's a separate issue.

[certik]

On Linux with /bin/cat, it seems to work:

~/repos/shell(ctrl_c2)$ /bin/cat
s
s
^CReceived Ctrl+C
~/repos/shell(ctrl_c2)$

But on the builtin cat it just hangs, will not exit. I must exit it with Ctrl-D.