[bsp/qemu-vexpress-a9] support function names in backtraces

[liulangrenaaa]

Pass -mpoke-function-name to the compiler and assembler when RT_BACKTRACE_FUNCTION_NAME is enabled for the Cortex-A9 QEMU BSP. Keep the BSP configuration opt-in so users can enable symbolized backtraces through menuconfig without changing the default build.

Validation:

• scons --pyconfig-silent
• scons -C bsp/qemu-vexpress-a9 -j2
• QEMU function-name backtrace verified with RT_BACKTRACE_FUNCTION_NAME enabled in a local configuration.

为什么提交这份PR (why to submit this PR)

qemu-vexpress-a9 BSP 默认没有开启函数名符号支持，导致启用 RT_BACKTRACE_FUNCTION_NAME 后 backtrace 仍然只能打印地址，无法直接显示函数名，调试体验较差。

你的解决方案是什么 (what is your solution)

在 bsp/qemu-vexpress-a9/SConstruct 中检测 rtconfig.h 是否定义了 RT_BACKTRACE_FUNCTION_NAME，若已启用则向编译器和汇编器追加 -mpoke-function-name 选项。该选项由 GCC ARM 提供，会把函数名嵌入 text 段，使 Cortex-A 的 backtrace 能直接输出函数名。此配置保持 opt-in，不影响默认构建。

请提供验证的bsp和config (provide the config and bsp)

• BSP: bsp/qemu-vexpress-a9
• .config: CONFIG_RT_BACKTRACE_FUNCTION_NAME=y
• action: （请在这里填上你自己仓库触发的 GitHub Actions 编译成功链接，例如 https://github.com/你的用户名/rt-thread/actions/runs/xxxxxx）

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用clang-format 源码格式化工具确保格式符合RT-Thread代码规范 This PR has been formatted with clang-format and complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

[github-actions]

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