gd: security bump to version 2.2.3

gd: security bump to version 2.2.3

Security related fixes:
This flaw is caused by loading data from external sources (file, custom ctx,
etc) and are hard to validate before calling libgd APIs:

- fix php bug 72339, Integer Overflow in _gd2GetHeader (CVE-2016-5766)
- bug #248, fix Out-Of-Bounds Read in read_image_tga
- gd: Buffer over-read issue when parsing crafted TGA file (CVE-2016-6132)

Using application provided parameters, in these cases invalid data causes
the issues:

 - Integer overflow error within _gdContributionsAlloc() (CVE-2016-6207)
 - fix php bug 72494, invalid color index not handled, can lead to crash ( CVE-2016-6128)
 - improve color check for CropThreshold

The build system now enables -Wall and -Werror by default, so pass
--disable-werror to disable that.  Notice that this issue has been fixed
upstream post-2.2.3:

https://github.com/libgd/libgd/issues/339

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>