LibC+Shell: Make system() actually work.

system() will now fork off a child process and execute the command via
/bin/sh -c. There are probably some things to fix here, but it's a start.

LibC/stdlib.cpp

@@ -206,7 +206,16 @@ void srandom(unsigned seed)
 
 int system(const char* command)
 {
-    return execl("/bin/sh", "sh", "-c", command, nullptr);
+    auto child = fork();
+    if (!child) {
+        int rc = execl("/bin/sh", "sh", "-c", command, nullptr);
+        if (rc < 0)
+            perror("execl");
+        exit(0);
+    }
+    int wstatus;
+    waitpid(child, &wstatus, 0);
+    return WEXITSTATUS(wstatus);
 }
 
 char* mktemp(char* pattern)

Shell/main.cpp

@@ -413,9 +413,10 @@ int main(int argc, char** argv)
         endpwent();
     }
 
-    if (argc > 1 && !strcmp(argv[1], "-c")) {
-        fprintf(stderr, "FIXME: Implement /bin/sh -c\n");
-        return 1;
+    if (argc > 2 && !strcmp(argv[1], "-c")) {
+        dbgprintf("sh -c '%s'\n", argv[2]);
+        run_command(argv[2]);
+        return 0;
     }
 
     {