Add QEMU based CI regression test infra for RV32 and RV64 (#526)

Added a QEMU virt-machine BSP and CTest infrastructure to run the
ThreadX regression suite on both RISC-V 32-bit and 64-bit targets
in CI.

New components:
- BSP (entry, trap, PLIC, CLINT timer, UART, linker script) targeting
  QEMU virt machine for RV32 and RV64
- CMake build system with Ninja, supporting multiple build configs
- CI scripts: install_riscv.sh (toolchain + QEMU), build_tx_riscv.sh,
  test_tx_riscv.sh
- GitHub Actions workflow job for RISC-V regression gating

Port fixes:
- RV32 tx_thread_context_restore.S: set MPIE alongside MPP (0x1800 →
  0x1880) so mret re-enables interrupts
- RV32/RV64 tx_port.h: add TX_REGRESSION_TEST extension macros needed
  by the test harness
- RV32/RV64 example_build scripts: add compile and QEMU launch steps

Regression test portability fixes:
- Block memory tests: increase pool sizes (320 → 340) to accommodate
  larger RISC-V block-header alignment
- Byte memory test: replace hardcoded offsets with BYTE_POOL_OVERHEAD
  macro for portable pool-size computation
- Event flag timeout test: make counter tolerance unconditional,
  removing linux-only guard

Signed-off-by: Akif Ejaz <akif.ejaz@10xengineers.ai>

scripts/build_tx_riscv.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+# Build RISC-V regression tests for both RV32 and RV64.
+# Usage: build_tx_riscv.sh [all|<config>]
+
+SCRIPT_DIR="$(dirname "$(realpath "$0")")"
+RUN_SH="${SCRIPT_DIR}/../test/tx/cmake/riscv/run.sh"
+
+ARGS="${@:-all}"
+
+echo "=== Building RISC-V32 ==="
+"$RUN_SH" riscv32 build $ARGS
+
+echo ""
+echo "=== Building RISC-V64 ==="
+"$RUN_SH" riscv64 build $ARGS

scripts/install_riscv.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+# Install RISC-V bare-metal cross-compiler toolchain and QEMU for CI.
+set -e
+
+RELEASE_TAG="2026.04.26"
+BASE_URL="https://github.com/riscv-collab/riscv-gnu-toolchain/releases/download/${RELEASE_TAG}"
+# Use ubuntu-24.04 binaries to match ubuntu-latest runners.
+RV32_TARBALL="riscv32-elf-ubuntu-24.04-gcc.tar.xz"
+RV64_TARBALL="riscv64-elf-ubuntu-24.04-gcc.tar.xz"
+
+echo "=== Installing QEMU and build tools ==="
+sudo apt-get update -qq
+sudo apt-get install -y -qq qemu-system-misc ninja-build cmake
+
+echo "=== Downloading RISC-V GCC toolchain (${RELEASE_TAG}) ==="
+
+# Both tarballs extract into riscv/ with non-overlapping prefixes
+# (riscv32-unknown-elf-* and riscv64-unknown-elf-*).
+for tarball in "$RV32_TARBALL" "$RV64_TARBALL"; do
+    echo "Downloading ${tarball} ..."
+    wget --no-verbose "${BASE_URL}/${tarball}" -O "/tmp/${tarball}"
+    sudo tar xJf "/tmp/${tarball}" -C /opt
+    rm "/tmp/${tarball}"
+done
+
+TOOLCHAIN_BIN=/opt/riscv/bin
+echo "$TOOLCHAIN_BIN" >> "$GITHUB_PATH"
+
+echo "=== Verifying installation ==="
+"$TOOLCHAIN_BIN/riscv32-unknown-elf-gcc" --version | head -1
+"$TOOLCHAIN_BIN/riscv64-unknown-elf-gcc" --version | head -1
+qemu-system-riscv64 --version | head -1

scripts/test_tx_riscv.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Run RISC-V regression tests for both RV32 and RV64 on QEMU.
+# Usage: test_tx_riscv.sh [all|<config>]
+
+SCRIPT_DIR="$(dirname "$(realpath "$0")")"
+RUN_SH="${SCRIPT_DIR}/../test/tx/cmake/riscv/run.sh"
+
+ARGS="${@:-all}"
+
+exit_code=0
+
+echo "=== Testing RISC-V32 ==="
+CTEST_PARALLEL_LEVEL=4 "$RUN_SH" riscv32 test $ARGS || exit_code=$?
+
+echo ""
+echo "=== Testing RISC-V64 ==="
+CTEST_PARALLEL_LEVEL=4 "$RUN_SH" riscv64 test $ARGS || exit_code=$?
+
+exit $exit_code