Firefox 101 on POWER

Firefox 101 is out, mostly of interest to developers but with a few liveability improvements. I suspect breakage of our LTO-PGO patch will be a regular occurrence and Fx101 indeed broke the diff again, but after updating rust, cargo and cbindgen the optimized build works fine with this revised PGO-LTO patch and the same .mozconfigs from Firefox 95.

I can't figure out where the bugs are in our POWER9 Ion JavaScript JIT implementation, though I still strongly suspect it's because we use sign-extended 32-bit ints. This is enough to pass the test suite but still breaks with the web. MIPS does too and we are strongly based on the MIPS port, but one wonders if MIPS suffers from the same issues, and I'm quite sure it's not tested anywhere near as well. As 32-bit arithmetic instructions aren't orthogonal in Power ISA this change would require some significant rearchitecting and I've just come off a really bad week at work, so I'll just try to pull up the current JIT to 102 so that those of you building the new ESR can continue to use Baseline Interpreter and Baseline Compiler, and then it will be time for more major surgery on the source code. You can help (please!).