No, you really can’t. For some OSS, on hardware that has an OS supported by that software, with a compiler that supports that target and the options you want, and in some cases where the OSS has been written to support those options, you can compile it. Otherwise you are just out of luck.

I don't really understand your position here. Compiler availability isn't really that big of a deal, even on obscure or proprietary platforms. Why would there be "some cases where the OSS has been written to support those options"?

> lots of commercial software is now compiled for newer x86 64 extensions.

Almost all software I encountered - including Windows 10 and precompiled Debian 13 - needs only SSE4.2, essentially mid-2000s ISA. Intel produced until very recently (early 2020s) Celeron CPUs which did not even support AVX.

People focus on AVX entirely too much, it is stuff like POPCNT that matters more. Which as you pointed out, is part of SSE4.2

...which has been with us almost 20 years.

Yet I still have regular conversations explaining "there is no way our customers are running on hardware that doesn't support this, where would they even be getting the hardware from, 2008?". I have a set of requirements in front of me requiring software to run on not only all Intel 64-bit chips, but also all Intel 32-bit chips.