Fixes -Wincompatible-pointer-type error by replacing RETSIGTYPE with void
This patch was made for the purposes of building CLFS-MIPS with newer compilers

diff -ru ncurses-5.9.orig/ncurses/tty/lib_tstp.c ncurses-5.9/ncurses/tty/lib_tstp.c
--- ncurses-5.9.orig/ncurses/tty/lib_tstp.c	2010-05-15 17:31:12.000000000 -0400
+++ ncurses-5.9/ncurses/tty/lib_tstp.c	2026-09-10 03:26:47.576907040 -0400
@@ -301,7 +301,7 @@
  * handler.
  */
 static int
-CatchIfDefault(int sig, RETSIGTYPE (*handler) (int))
+CatchIfDefault(int sig, void (*handler) (int))
 {
     int result;
 #if HAVE_SIGACTION || HAVE_SIGVEC
@@ -331,7 +331,7 @@
 	result = FALSE;
     }
 #else /* !HAVE_SIGACTION */
-    RETSIGTYPE (*ohandler) (int);
+    void (*ohandler) (int);
 
     ohandler = signal(sig, SIG_IGN);
     if (ohandler == SIG_DFL