Summary

This PR brings ARM64 dynarec 3DNow handling to parity with the 3DNow scope currently implemented in 86Box’s interpreter

Scope clarification:

• This PR targets parity with 86Box’s existing implemented 3DNow subset.
• It does not claim implementation of every historical 3DNow-family ISA variant beyond what 86Box currently models.

Current coverage state in this branch:

• Interpreter: full coverage of 86Box’s implemented 3DNow scope.
• ARM64 dynarec: parity with interpreter for that scope.
• x86-64 dynarec: still has fallback gaps in parts of the same scope.

Practical outcome:

• No regressions observed in local workload validation.
• ARM64 dynarec now covers the implemented 3DNow surface; previously missing ARM64 cases fell back to interpreter execution

ARM64 dynarec/codegen fixes and cleanup to stabilize and improve NDR behavior on ARM64 while keeping behavior aligned with existing paths.

Main changes in this PR:

• ARM64/backend/codegen updates across:
  • src/codegen_new/codegen*.{c,h}
  • src/codegen_new/codegen_backend_arm64*.{c,h}
  • src/codegen_new/codegen_ops*.{c,h}
  • src/cpu/386_dynarec.c
  • src/cpu/x86_ops_3dnow.h
  • src/86box.c
• Qt-side runtime/pacing related adjustments in:
  • src/qt/qt_main.cpp
  • src/qt/qt_mainwindow.cpp
  • src/qt/qt_platform.cpp

runtime/pacing changes should help all platforms.

Notes:

• Scope is intentionally limited to the modified source file set in this branch.
• No ROM or asset changes are required.

Checklist

• I have tested my changes locally and validated that the functionality works as intended
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
• I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/
• This pull request requires changes to the asset set
• I have opened an assets pull request - https://github.com/86Box/assets/pull/changeme/