Implement signal_watchdog, a child-process checker for dangerous functions.

• Create signal_watchdog.c.
• Expose int signal_watchdog(void (*fn)(void), unsigned int timeout, bool verbose);.
• Run fn in a child process.
• Return 1 when the child exits normally with status 0 before the timeout.
• Return 0 when the child exits with another status, is stopped or killed by a signal, or reaches the timeout.
• Return -1 when the watchdog itself cannot set up the child or signal handling.
• When verbose is false, do not print anything.
• When verbose is true and the function is good, print exactly Good function followed by a newline.
• When verbose is true and the child exits with a non-zero status, print exactly Bad function: exit <code> followed by a newline.
• When verbose is true and the child is stopped or killed by a signal, print exactly Bad function: <signal description> followed by a newline.
• When verbose is true and the timeout is reached, print exactly Bad function: timeout after <timeout> seconds followed by a newline.
• Do not leave a running or zombie child behind, including timeout cases.

Implement signal_watchdog, a child-process checker for dangerous functions.

• Create signal_watchdog.c.
• Expose int signal_watchdog(void (*fn)(void), unsigned int timeout, bool verbose);.
• Run fn in a child process.
• Return 1 when the child exits normally with status 0 before the timeout.
• Return 0 when the child exits with another status, is stopped or killed by a signal, or reaches the timeout.
• Return -1 when the watchdog itself cannot set up the child or signal handling.
• When verbose is false, do not print anything.
• When verbose is true and the function is good, print exactly Good function followed by a newline.
• When verbose is true and the child exits with a non-zero status, print exactly Bad function: exit <code> followed by a newline.
• When verbose is true and the child is stopped or killed by a signal, print exactly Bad function: <signal description> followed by a newline.
• When verbose is true and the timeout is reached, print exactly Bad function: timeout after <timeout> seconds followed by a newline.
• Do not leave a running or zombie child behind, including timeout cases.