Search $PATH for the shutdown binary instead of hard-coding /sbin/shutdown,
which isn't valid on NixOS (and a compatibility link on most other modern
distros anyway).

  -- nckx <github@tobias.gr>
--- a/include/pathnames.h
+++ b/include/pathnames.h
@@ -53,7 +53,7 @@
 #ifndef _PATH_LOGIN
 #define _PATH_LOGIN		"/bin/login"
 #endif
-#define _PATH_SHUTDOWN		"/sbin/shutdown"
+#define _PATH_SHUTDOWN   "shutdown"

 #define _PATH_TERMCOLORS_DIRNAME "terminal-colors.d"
 #define _PATH_TERMCOLORS_DIR	"/etc/" _PATH_TERMCOLORS_DIRNAME
--- a/sys-utils/rtcwake.c
+++ b/sys-utils/rtcwake.c
@@ -575,7 +575,7 @@ int main(int argc, char **argv)
 		arg[i++] = "now";
 		arg[i]   = NULL;
 		if (!ctl.dryrun) {
-			execv(arg[0], arg);
+			execvp(arg[0], arg);
 			warn(_("failed to execute %s"), _PATH_SHUTDOWN);
 			rc = EXIT_FAILURE;
 		}