Make Process do prctl(PR_SET_PDEATHSIG)

This means that nanosm managed process will also predictably die if nanosm is killed.

src/Process.cpp

@@ -3,6 +3,7 @@
 #include <linux/sched.h>
 #include <sched.h>
 #include <signal.h>
+#include <sys/prctl.h>
 #include <sys/types.h>
 
 #include "WordExp.hpp"
@@ -49,6 +50,12 @@ namespace nanosm {
 			for(usize i = 0; i < exp.words.size(); ++i)
 				argv[i] = exp.words[i].data();
 
+			// Ensure that if nanosm (the parent) dies, we die along with it
+			if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
+				perror("Process pre-exec: prctl(PR_SET_PDEATHSIG)");
+				exit(1);
+			}
+
 			exit(execvp(exp.words[0].data(), argv.data()));
 		} else {
 			// Parent: monitor the pidfd by adding ourselves to the event loop now