PHP 4.0.5 compilation breaks when building GD with GD 1.5 (the last version with official GIF support), with an error message reporting gdImageGifCtx as undefined. It seems GD detects that GD 1.5 has IOCTX support, but incorrectly assumes that the GIF IOCTX filter (available only with certain unofficial patched versions of GD 1.8.x) is also available.

Applying the following patch will fix the problem, but there is probably a cleaner solution:

*** gd.c~	Mon Mar 12 05:57:53 2001
--- gd.c	Tue May  1 15:41:50 2001
***************
*** 911,917 ****
  PHP_FUNCTION(imagegif)
  {
  #ifdef HAVE_GD_GIF
! #ifdef USE_GD_IOCTX
  	_php_image_output_ctx(INTERNAL_FUNCTION_PARAM_PASSTHRU, PHP_GDIMG_TYPE_GIF, "GIF", gdImageGifCtx);
  #else
  	_php_image_output(INTERNAL_FUNCTION_PARAM_PASSTHRU, PHP_GDIMG_TYPE_GIF, "GIF", gdImageGif);
--- 911,917 ----
  PHP_FUNCTION(imagegif)
  {
  #ifdef HAVE_GD_GIF
! #ifdef USE_GD_IOCTX_GIF
  	_php_image_output_ctx(INTERNAL_FUNCTION_PARAM_PASSTHRU, PHP_GDIMG_TYPE_GIF, "GIF", gdImageGifCtx);
  #else
  	_php_image_output(INTERNAL_FUNCTION_PARAM_PASSTHRU, PHP_GDIMG_TYPE_GIF, "GIF", gdImageGif);