Why are the builds failing then?

planned obsolescence by Google

Beginning to use a CPU opcode that is 19 years old doesn't feel like planned obsolescence. if anything, it feels like unplanned obsolescence... "Oh hell what do you mean your CPU doesn't have that opcode no we've just been running the compiler with the default flags and that opcode got added to the default two months ago after a 10-year fight about the possible consequences of changing defaults!"

Although I'm a little surprised to learn that the binary itself doesn't have enough information in its header to be able to declare that it needs SSSE3 to be executed; that feels like something that should be statically-analyzed-and-cached to avoid a lot of debugging headaches.

> "Oh hell what do you mean your CPU doesn't have that opcode [...]"

hobbyst dev? sure

Google? nope

Did they make any explicit guarantees that their newly-cut binaries would continue to support 20-year-old architectures?

Googlers aren't gods. It's a 100,000-person company; they're as vulnerable to "We didn't really think of that one way or the other" as anyone else.

They clearly don't