[x265] Fix signal handler

[SF Markus Elfring]

Hello,

1. The data type of the variable "local" should be "sig_atomic_t" for better
portability.
   https://bitbucket.org/multicoreware/x265/src/d11de33521cf/source/x265.cpp#cl-79

2. The function "exit" does not belong to the list of async-signal-safe functions.

https://www.securecoding.cert.org/confluence/display/cplusplus/SIG30-CPP.+Call+only+asynchronous-safe+functions+within+signal+handlers

  I guess that a different program design will be needed for your function
"sigint_handler".

Regards,
Markus