Add RISCOF compliance test support

[jserv]

This implements complete support for RISC-V architectural compliance tests that use the tohost/fromhost protocol.

• Add check_tohost_write() function to detect writes to tohost address
• Extract tohost/fromhost symbol addresses from ELF during init
• Add tohost detection hooks to all store instructions:
  • Basic stores: SB, SH, SW
  • Atomic operations: SC.W, AMOSWAP.W, AMOADD.W, AMOXOR.W, AMOAND.W, AMOOR.W, AMOMIN.W, AMOMAX.W, AMOMINU.W, AMOMAXU.W
  • Floating point: FSW
  • Compressed: C.SW, C.SWSP, C.FSW, C.FSWSP
  • Fused operations: Multiple SW fusion
• Remove exit code truncation to preserve full test numbers
• Add tohost_addr/fromhost_addr fields to riscv_t structure

All changes are conditionally compiled with RV32_HAS(ARCH_TEST) to ensure zero overhead when the feature is disabled. The implementation follows the RISC-V tohost protocol: tests write exit code to tohost (extracted as value >> 1) and enter infinite loop.

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Summary by cubic

Add full RISC-V architectural (RISCOF) compliance test support using the tohost/fromhost protocol. The emulator now detects tohost writes, halts, and returns the correct exit code.

• New Features
  • Parse tohost/fromhost symbol addresses from the ELF at startup when arch-test mode is enabled.
  • Detect writes to tohost across all store paths (SB/SH/SW, AMO/SC.W, FSW, compressed stores, fused multi-SW) and halt with exit_code = value >> 1.
  • Preserve full exit codes (no truncation).
  • Add tohost_addr/fromhost_addr fields and setter APIs on riscv_t.
  • Fully gated behind RV32_HAS(ARCH_TEST) for zero overhead when disabled.

^{Written for commit 0767f16. Summary will update automatically on new commits.}

[jserv]

Benchmarks

Benchmark suite	Current: 0767f16	Previous: 0a8c53c	Ratio
Dhrystone	1315 Average DMIPS over 10 runs	1265 Average DMIPS over 10 runs	0.96
Coremark	911.157 Average iterations/sec over 10 runs	902.645 Average iterations/sec over 10 runs	0.99

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