upgrade vendored libtiff to 4.6.0 for SDL3_image

[sezero]

This will make us track latest libtiff with all bug fixes already in. I created a v4.6.0-SDL branch with two commits cherry-picked from master.

CC: @madebr: Can you prepare the rest, e.g. cmake'ry and such?

[madebr]

I pushed 2 little patches to make integration in SDL_image as frictionless as possible.

btw, libsdl-org/libtiff@0a44dce is not really needed for SDL_image's purpose.
It's only useful when you install a complete libtiff sdk, including headers and libraries. SDL_image does not install any tiff headers and/or win32 tiff import libraries.

[sezero]

OK, it's ready then?

[sezero]

P.S.: @slouken: Android.mk doesn't even mention tiff: We don't want to support tiff in android builds, or is it an oversight?

[madebr]

OK, it's ready then?

I tried building with my native toolchain + mingw, and it works. So you have a go from me :)