patch 8.2.4201: when using the GUI CTRL-Z does not stop gvim

Problem:    When using the GUI CTRL-Z does not stop gvim.
Solution:   When using the GUI set SIGTSTP to SIG_DFL. (Andrew Maltsev,
            closes #9570)

src/os_unix.c

@@ -1378,7 +1378,14 @@ set_signals(void)
 
 #ifdef SIGTSTP
     // See mch_init() for the conditions under which we ignore SIGTSTP.
-    signal(SIGTSTP, ignore_sigtstp ? SIG_IGN : (RETSIGTYPE (*)())sig_tstp);
+    // In the GUI default TSTP processing is OK.
+    // Checking both gui.in_use and gui.starting because gui.in_use is not set
+    // at this point (set after menus are displayed), but gui.starting is set.
+    signal(SIGTSTP, ignore_sigtstp ? SIG_IGN
+# ifdef FEAT_GUI
+				: gui.in_use || gui.starting ? SIG_DFL
+# endif
+				    : (RETSIGTYPE (*)())sig_tstp);
 #endif
 #if defined(SIGCONT)
     signal(SIGCONT, sigcont_handler);

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4201,
 /**/
     4200,
 /**/