Avoid implicit ints and implicit function declarations.  These
language features have been removed from C in 1999. Future compilers
are likely to stop accepting these constructs by default.

Submitted upstream: <https://github.com/eserte/perl-tk/pull/91>

diff -ur Tk-804.036.orig/config/signedchar.c Tk-804.036/config/signedchar.c
--- Tk-804.036.orig/config/signedchar.c	2023-02-24 10:48:08.060779006 +0100
+++ Tk-804.036/config/signedchar.c	2023-02-24 10:48:58.315268904 +0100
@@ -1,4 +1,4 @@
-main()
+int main(void)
 {
  signed char x = 'a';
  return (x - 'a');
diff -ur Tk-804.036.orig/config/unsigned.c Tk-804.036/config/unsigned.c
--- Tk-804.036.orig/config/unsigned.c	2023-02-24 10:48:08.054779067 +0100
+++ Tk-804.036/config/unsigned.c	2023-02-24 10:49:27.580971854 +0100
@@ -1,15 +1,16 @@
+#include <stdio.h>
 int main()
 {
  char x[] = "\377";
  if (x[0] > 0)
   {
    printf("char is unsigned type\n");
-   exit(0);
+   return 0;
   }
  else
   {
    printf("char is signed type\n");
-   exit(1);
+   return 1;
   }
 }
 
diff -ur Tk-804.036.orig/pTk/config/Hstrdup.c Tk-804.036/pTk/config/Hstrdup.c
--- Tk-804.036.orig/pTk/config/Hstrdup.c	2023-02-24 10:48:08.010779514 +0100
+++ Tk-804.036/pTk/config/Hstrdup.c	2023-02-24 10:53:04.326771841 +0100
@@ -6,7 +6,7 @@
 {char *e;
  char *p = strdup(STRING);
  if (!p || strcmp(p,STRING))
-  exit(1);
+  return 1;
  return 0;
 }
 
diff -ur Tk-804.036.orig/pTk/config/Hstrtoul.c Tk-804.036/pTk/config/Hstrtoul.c
--- Tk-804.036.orig/pTk/config/Hstrtoul.c	2023-02-24 10:48:08.013779483 +0100
+++ Tk-804.036/pTk/config/Hstrtoul.c	2023-02-24 10:50:13.205508745 +0100
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 
 int main()
 {char *e;
diff -ur Tk-804.036.orig/pTk/mTk/generic/tkEvent.c Tk-804.036/pTk/mTk/generic/tkEvent.c
--- Tk-804.036.orig/pTk/mTk/generic/tkEvent.c	2023-02-24 10:48:07.324786476 +0100
+++ Tk-804.036/pTk/mTk/generic/tkEvent.c	2023-02-24 10:54:20.859995000 +0100
@@ -1153,6 +1153,7 @@
 Time
 TkCurrentTime(dispPtr, fallbackCurrent)
     TkDisplay *dispPtr;		/* Display for which the time is desired. */
+    int fallbackCurrent;
 {
     register XEvent *eventPtr;
     ThreadSpecificData *tsdPtr = (ThreadSpecificData *)
diff -ur Tk-804.036.orig/pTk/mTk/generic/tkImage.c Tk-804.036/pTk/mTk/generic/tkImage.c
--- Tk-804.036.orig/pTk/mTk/generic/tkImage.c	2023-02-24 10:48:07.321786507 +0100
+++ Tk-804.036/pTk/mTk/generic/tkImage.c	2023-02-24 10:55:56.174027554 +0100
@@ -1083,6 +1083,8 @@
 int y;
 int width;
 int height;
+int imgWidth;
+int imgHeight;
 {
     Tk_Tile tile = (Tk_Tile) clientData;
     Tk_TileChange *handler;