wayland: Add a sigtimedwait() implementation for OpenBSD

sigtimedwait() is an optional part of POSIX.1-2001, and OpenBSD doesn't implement it. Add a replacement implementation based on https://comp.unix.programmer.narkive.com/rEDH0sPT/sigtimedwait-implementation

(backported from commit 1049426a76)

configure

@@ -19755,6 +19755,12 @@ if test "x$ac_cv_func_sigaction" = xyes
 then :
   printf "%s\n" "#define HAVE_SIGACTION 1" >>confdefs.h
 
+fi
+ac_fn_c_check_func "$LINENO" "sigtimedwait" "ac_cv_func_sigtimedwait"
+if test "x$ac_cv_func_sigtimedwait" = xyes
+then :
+  printf "%s\n" "#define HAVE_SIGTIMEDWAIT 1" >>confdefs.h
+
 fi
 ac_fn_c_check_func "$LINENO" "setjmp" "ac_cv_func_setjmp"
 if test "x$ac_cv_func_setjmp" = xyes
@@ -22422,7 +22428,6 @@ printf %s "checking for NAS audio support... " >&6; }
             have_nas=yes
             NAS_CFLAGS="-I/usr/X11R6/include/"
             NAS_LIBS="-L/usr/X11R6/lib -laudio -lXt"
-
         fi
 
         { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $have_nas" >&5