SPECS: gd: Align optional codec options

[Jingwiw]

Changes

• Add the missing remote asset checksum for the gd source archive.

• Make the optional AVIF, WebP, and XPM codec choices explicit when their bconds are disabled.

  These bconds default to disabled in the spec, but upstream defaults feature checks to auto when no --with/--without value is passed.

  Source: configure.ac

  m4_define([GD_LIB_CHECK], [dnl
    ...
    AC_ARG_WITH([$3],
      [AS_HELP_STRING([--with-$3@<:@=DIR@:>@], [Support $3 (optionally in DIR)])],
      [gd_with_lib=$withval],
      [gd_with_lib=auto])
    AC_MSG_RESULT([$gd_with_lib])
  
    gd_found_lib=no
    gd_require_pkg_name=""
    if test "$gd_with_lib" != "no"; then

  Source: configure.ac

  dnl Check for xpm support.
  GD_LIB_PKG_CHECK([LIBXPM], [XPM], [xpm], [xpm], [
    ...
  ])
  
  dnl Check for webp support.
  GD_LIB_PKG_CHECK([LIBWEBP], [WEBP], [webp], [libwebp >= 0.2.0], [
    ...
  ])
  
  dnl Check for avif support.
  GD_LIB_PKG_CHECK([LIBAVIF], [AVIF], [avif], [libavif >= 0.8.2], [
    ...
  ])

• Drop the misspelled --disable-slient-rules configure option.

  The package build log reported it as an unrecognized option, and the autotools build path already passes the correctly spelled --disable-silent-rules.

• Use %autochangelog directly, matching the current spec style.

AIGC Declaration: CodeX with gpt5.5 was used as coding agent.

Signed-off-by: Jingwiw wangjingwei@iscas.ac.cn