libpng: Enable intrinsics on x86/SSE2, ppc64/VSX, and all arm/NEON #7701

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 23s
🤖 Android / Template (target=template_release)	1h 2m 50s
🌐 Web / Template (target=template_release)	21m 49s
🍎 macOS / Editor (target=editor, tests=yes)	45m 6s
🍎 macOS / Template (target=template_release)	31m 49s
🍏 iOS / Template (target=template_release)	24m 39s
🏁 Windows / Editor (target=editor, tests=yes)	1h 46m 40s
🏁 Windows / Template (target=template_release)	57m 30s
🐧 Linux / Editor w/ Mono (target=editor)	1h 8m 28s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	1h 9m 43s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	41m 23s
🐧 Linux / Template w/ Mono (target=template_release)	35m 40s
🐧 Linux / Minimal template (target=template_release, everything disabled)	28m 18s
🪲 Godot CPP / Build and test Godot CPP	11m 27s
	10h 6m 45s

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