Revert "Remove dmenumon variable"

This reverts commit c2b748e793.

Revert back this change. It seems to not be an edge-case anymore since
multiple users have asked about this new behaviour now.

config.def.h

@@ -56,7 +56,8 @@ static const Layout layouts[] = {
 #define SHCMD(cmd) { .v = (const char*[]){ "/bin/sh", "-c", cmd, NULL } }
 
 /* commands */
-static const char *dmenucmd[] = { "dmenu_run", "-fn", dmenufont, "-nb", col_gray1, "-nf", col_gray3, "-sb", col_cyan, "-sf", col_gray4, NULL };
+static char dmenumon[2] = "0"; /* component of dmenucmd, manipulated in spawn() */
+static const char *dmenucmd[] = { "dmenu_run", "-m", dmenumon, "-fn", dmenufont, "-nb", col_gray1, "-nf", col_gray3, "-sb", col_cyan, "-sf", col_gray4, NULL };
 static const char *termcmd[]  = { "st", NULL };
 
 static const Key keys[] = {

dwm.c

@@ -1639,6 +1639,8 @@ sigchld(int unused)
 void
 spawn(const Arg *arg)
 {
+	if (arg->v == dmenucmd)
+		dmenumon[0] = '0' + selmon->num;
 	if (fork() == 0) {
 		if (dpy)
 			close(ConnectionNumber(dpy));