Failing tests with external libgd

Description

I was experimenting with using the system gd for our Gentoo package, and noticed a bunch of test failures:

Bug #38212 (Seg Fault on invalid imagecreatefromgd2part() parameters) [ext/gd/tests/bug38212-mb.phpt]
Bug #38212 (Seg Fault on invalid imagecreatefromgd2part() parameters) [ext/gd/tests/bug38212.phpt]
Bug #39780 (PNG image with CRC/data error raises a fatal error) [ext/gd/tests/bug39780_extern.phpt]
Bug #41442 (imagegd2() under output control) [ext/gd/tests/bug41442.phpt]
Bug #43073 (TrueType bounding box is wrong for angle<>0) [ext/gd/tests/bug43073.phpt]
Bug #45799 (imagepng() crashes on empty image). [ext/gd/tests/bug45799.phpt]
Bug #48732 (TTF Bounding box wrong for letters below baseline) [ext/gd/tests/bug48732-mb.phpt]
Bug #48732 (TTF Bounding box wrong for letters below baseline) [ext/gd/tests/bug48732.phpt]
Bug #48801 (Problem with imagettfbbox) [ext/gd/tests/bug48801-mb.phpt]
Bug #48801 (Problem with imagettfbbox) [ext/gd/tests/bug48801.phpt]
Bug #53504 imagettfbbox/imageftbbox gives incorrect values for bounding box [ext/gd/tests/bug53504.phpt]
Bug #65148 (imagerotate may alter image dimensions) [ext/gd/tests/bug65148.phpt]
Bug #66356 (Heap Overflow Vulnerability in imagecrop()) [ext/gd/tests/bug66356.phpt]
Bug #71912 (libgd: signedness vulnerability) [ext/gd/tests/bug71912-mb.phpt]
Bug #71912 (libgd: signedness vulnerability) [ext/gd/tests/bug71912.phpt]
Bug #72339 Integer Overflow in _gd2GetHeader() resulting in heap overflow [ext/gd/tests/bug72339.phpt]
Bug #73155 (imagegd2() writes wrong chunk sizes on boundaries) [ext/gd/tests/bug73155.phpt]
Bug #73157 (imagegd2() ignores 3rd param if 4 are given) [ext/gd/tests/bug73157.phpt]
Bug #73159 (imagegd2(): unrecognized formats may result in corrupted files) [ext/gd/tests/bug73159.phpt]
Bug #73161 (imagecreatefromgd2() may leak memory) [ext/gd/tests/bug73161.phpt]
Bug #73272 (imagescale() is not affected by, but affects imagesetinterpolation()) [ext/gd/tests/bug73272.phpt]
Bug 73868 (DOS vulnerability in gdImageCreateFromGd2Ctx()) [ext/gd/tests/bug73868.phpt]
Bug #73869 (Signed Integer Overflow gd_io.c) [ext/gd/tests/bug73869.phpt]
Bug #77272 (imagescale() may return image resource on failure) [ext/gd/tests/bug77272.phpt]
Bug #77479 (imagewbmp() segfaults with very large image) [ext/gd/tests/bug77479.phpt]
Bug #77973 (Uninitialized read in gdImageCreateFromXbm) [ext/gd/tests/bug77973.phpt]
Bug #79676 (imagescale adds black border with IMG_BICUBIC) [ext/gd/tests/bug79676.phpt]
Test max colors for a gd image. [ext/gd/tests/crafted_gd2.phpt]
imagecreatefromgd2 [ext/gd/tests/createfromgd2.phpt]
imagecreatefromwbmp with invalid wbmp [ext/gd/tests/createfromwbmp2_extern.phpt]
gif --> gd1/gd2 conversion test [ext/gd/tests/gif2gd.phpt]
imagegd() writes truecolor images without palette conversion [ext/gd/tests/imagegd_truecolor.phpt]
imagegetinterpolation() and imagesetinterpolation() basic test [ext/gd/tests/imageinterpolation_basic.phpt]
Scale images and preserve aspect ratio [ext/gd/tests/imagescale_preserve_ratio.phpt]
jpeg <--> gd1/gd2 conversion test [ext/gd/tests/jpg2gd-mb.phpt]
jpeg <--> gd1/gd2 conversion test [ext/gd/tests/jpg2gd.phpt]
libgd #86 (Possible infinite loop in imagecreatefrompng) [ext/gd/tests/libgd00086_extern.phpt]
png <--> gd1/gd2 conversion test [ext/gd/tests/png2gd.phpt]
xpm --> gd1/gd2 conversion test [ext/gd/tests/xpm2gd.phpt]

These fall into a few classes, some more difficult than others.

1. Tests using the "gd" image format. The "gd" format was removed from libgd-2.3.3 (https://github.com/libgd/libgd/blob/master/CHANGELOG.md#233---2021-09-12). I think most of these tests are obsolete and can simply be deleted.
2. Tests where the output is slightly different. For example, bug45799.phpt is looking for Warning: imagepng(): gd-png error: no colors in palette in %s on line %d but gets Warning: imagepng(): gd-png error: no colors in palette\n in %s on line %d. These tests could be made to support both outputs.
3. Fundamental behavior changes that never made it upstream. I'm not sure how many of these there are, or how important they are, but they're obviously the hard ones to fix. Less important ones might simply be dropped; but useful ones should probably go upstream.

PHP Version

git master

Operating System

No response

Start by running the listed ext/gd/tests with external libgd and group the failures into removed gd-format tests, output differences, and fundamental behavior changes. Review the affected .phpt files, beginning with bug45799.phpt and the gd conversion tests, then determine which tests can be removed, accept both outputs, or require an upstream fix. Done means the external-libgd test set has an explicit resolution for each failure.