Fix for `bun` crash, some rv64 / riscv64 / risc-v support improvements

[spital]

Playing a bit with chatGPT, got some results, still a way to go to have bun x64 running on riscv64 target.

root@9e17342373bd:/shared# ./box64_clang_mold_rel_dynarec/box64 --version
Box64 riscv64 v0.4.1 nogit with Dynarec with trace built on Apr 11 2026 06:59:23
root@9e17342373bd:/shared# for dir1 in ./bun-linux-x64-baseline.1.1.35 ./bun-linux-x64-baseline.1.2.14 ./bun-linux-x64-baseline.1.3.1 ./bun-linux-x64-baseline.1.3.12; do BOX64_LD_LIBRARY_PATH=/opt/x64root/usr/lib/x86_64-linux-gnu BOX64_EMULATED_LIBS=libc.so.6 ./box64_clang_mold_rel_dynarec/box64 $dir1/bun --version 2>/dev/null;done
1.1.35
1.2.14
1.3.1
1.3.12

Next I need to move to real hardware and test properly.
Is there any interest in PR for improved RISC-V support ?

[ptitSeb]

There is interestest in PR to improve RV64 support, but 100% AI generated code is not allowed. Every submited code must be understand by the human submiting the PR (and human in required to interact with us).

Also, what is "bun"?

[spital]

Bun is a fast, all-in-one JavaScript runtime toolkit:
* Includes native bundler, transpiler, task runner, and npm client
* Aims for 100% Node.js compatibility
* Can bundle, install, and run JavaScript & TypeScript

https://imagedelivery.betterstackcdn.com/xZXo0QFi-1_4Zimer-T0XQ/35f5b56e-a962-42f9-f287-460e1eef0c00/orig

ok. we'll see. gpt credits out :D