update qemu prebuilt to qemu 9.2

[enh-google]

qemu 9.2 has sifive's patches for significantly faster V that should let us start using more V.

we should also start enabling other extensions.

Zfa would let enh@ simplify some assembler.

Zicfilp and Zicfiss would let us start testing CFI.

[enh-google]

Zicbom would let ART do cache flushes.

[SiFiveHolland]

Zicbom would let ART do cache flushes.

Zicbom isn't currently exposed to userspace. See this thread on the LKML: https://lore.kernel.org/linux-riscv/20241025091527.57825-1-cuiyunhui@bytedance.com/

[enh-google]

Zicbom would let ART do cache flushes.

Zicbom isn't currently exposed to userspace. See this thread on the LKML: https://lore.kernel.org/linux-riscv/20241025091527.57825-1-cuiyunhui@bytedance.com/

ah, the same only-this-core problem that required __riscv_flush_icache(). thanks for pointing that out!

Zicfilp and Zicfiss would let us start testing CFI.

(it was pointed out to me elsewhere that the kernel support for this hasn't landed yet either.)