Implemented lazy FPU, GP relaxation, and QEMU automation for GNU port in arch/risc-v32 (#513)

This PR adds three functional improvements to the RISC-V 32-bit GNU port.

Lazy FPU stacking (tx_thread_context_save.S, tx_thread_context_restore.S, tx_thread_schedule.S): FP register save/restore is now skipped whenmstatus.FS is Off, reducing context switch overhead for threads that do not use floating point.

GP relaxation (cmake/riscv32_gnu.cmake, entry.s, link.lds): Enables the -mrelax compiler flag and defines __global_pointer$ in the linker script.The entry stub initializes gp at startup. gp is not saved or restored during context switches.

WFI in idle loop (tx_thread_schedule.S): The scheduler issues wfi when no thread is ready, replacing busy-waiting with a low-power sleep.

A Python/QEMU/GDB functional test runner is added under ports/risc-v32/gnu/example_build/qemu_virt/test/. It validates context switching, FPUcontext preservation, timer interrupts, and preemption. To run:

cd ports/risc-v32/gnu/example_build/qemu_virt
make check-functional-riscv32

Tested on QEMU virt machine (rv32gc).

Co-authored-by: Wei-Chen Lai [email protected]
Co-authored-by: Frédéric Desbiens [email protected]
Co-authored-by: Copilot [email protected]

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