Userland+LibC: Add "kill -l" to show all known signal names/numbers

Libraries/LibC/signal.cpp

@@ -236,4 +236,13 @@ int getsignalbyname(const char* name)
     errno = EINVAL;
     return -1;
 }
+
+const char* getsignalname(int signal)
+{
+    if (signal < 0 || signal >= NSIG) {
+        errno = EINVAL;
+        return nullptr;
+    }
+    return signal_names[signal];
+}
 }

Libraries/LibC/signal.h

@@ -76,6 +76,7 @@ int sigpending(sigset_t*);
 int sigsuspend(const sigset_t*);
 int raise(int sig);
 int getsignalbyname(const char*);
+const char* getsignalname(int);
 
 extern const char* sys_siglist[NSIG];
 

Userland/kill.cpp

@@ -46,6 +46,16 @@ int main(int argc, char** argv)
         return 1;
     }
 
+    if (argc == 2 && !strcmp(argv[1], "-l")) {
+        for (size_t i = 0; i < NSIG; ++i) {
+            if (i && !(i % 5))
+                outln("");
+            new_out("{:2}) {:10}", i, getsignalname(i));
+        }
+        outln("");
+        return 0;
+    }
+
     if (argc != 2 && argc != 3)
         print_usage_and_exit();
     unsigned signum = SIGTERM;