Build fails on Linux (GCC 15): SentencePiece missing <cstdint> + Highway avx10.2-512 errors

# Summary

Building gemma.cpp on Linux with GCC 15 fails due to issues in third-party dependencies:
1. CMake fails version check
2. sentencepiece headers fail to compile due to missing include

# Environment

* OS: Arch Linux
* cmake: 4.1.2
* clang: 21.1.6
* gcc: 15.2.1
* gemma.cpp: latest main (Nov 2025)

# Workaround Build steps

### 1) Specify clang and cmake version compatibility

`CC=clang CXX=clang++ cmake --preset make -DCMAKE_POLICY_VERSION_MINIMUM=3.5`

### 2) Add missing include in sentencepiece

`sed -i '24i #include ' build/_deps/sentencepiece-src/src/sentencepiece_processor.h`

### 3) Build

`cmake --build --preset make -j$(nproc)`

使用 issue 中的命令，借助 GCC 15、Clang 21、CMake 4.1.2 和 `make` 预设复现 Linux 构建。检查 CMake 版本检查以及 `build/_deps/sentencepiece-src/src/sentencepiece_processor.h`，然后调查报告的 Highway AVX10.2-512 错误。当 `cmake --build --preset make` 无需文档中记录的变通方法即可成功执行时，即表示完成。

由索引模型根据 Issue 内容生成。