Add Windows platform support with complete abstraction layer

[Copilot]

The mqttclient library had no Windows platform adaptation layer. All platform-specific code (threading, mutexes, sockets, timers) was Linux-only with pthread dependencies.

Platform Abstraction Layer

Created platform/windows/ with Win32 API implementations:

• Memory: standard C allocation
• Mutex: CRITICAL_SECTION
• Thread: CreateThread with event-based lifecycle
• Timer: QueryPerformanceCounter for microsecond precision
• Network: Winsock2 with thread-safe initialization

Automatic Platform Detection

Fixed critical constant definition order bug:

The platform constants (SALOF_USING_WINDOWS, etc.) were defined in salof_defconfig.h after including salof_config.h, but the detection code in salof_config.h needed those constants. This caused all Windows builds to be misdetected as Linux.

// Before (broken): Constants defined too late
#include "salof_config.h"
#define SALOF_USING_WINDOWS 5  // Used by code above!

// After (fixed): Constants defined first
#define SALOF_USING_WINDOWS 5
#include "salof_config.h"

Implemented three-layer detection:

1. salof_config.h: Primary detection via _WIN32, __linux__, etc.
2. mqtt_config.h: Fallback with #ifndef guard to prevent redefinition
3. salof_defconfig.h: Final safety check with error on unknown platform

Build System Updates

• Platform-specific compiler flags (MSVC /W3 /O2 vs GCC -Wall -O3)
• Correct static library extensions (.lib on Windows vs .a on Linux)
• Automatic platform directory selection in CMake
• Updated minimum CMake version to 3.10

Windows-Specific Issues Fixed

Winsock conflicts: Added WIN32_LEAN_AND_MEAN and _WINSOCKAPI_ guards to ensure winsock2.h takes precedence over old winsock.h

TLS disabled: mbedtls compilation on Windows has extensive issues. Disabled TLS entirely on Windows (TCP-only mode).

Cross-platform examples: All examples now use conditional compilation:

#if defined(_WIN32)
    #include <windows.h>
    #define sleep(x) Sleep((x)*1000)
    typedef HANDLE pthread_t;
#else
    #include <pthread.h>
#endif

Testing

Linux builds verified - no regressions. Windows builds require user testing in actual Windows environment.

Original prompt

---

This section details on the original issue you should resolve

<issue_title> platform 目录下找不到适配 windows 的文件</issue_title>
<issue_description>公司项目是使用 VS Studio C++开发，需要增加 mqtt 通信功能，看软件介绍可以支持windows，但在 platform 目录下却找不到适配 windows 的文件。是要自己来写windows平台的适配函数，还是有什么方法？
</issue_description>

<agent_instructions>实现以下windows中适配的代码
</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@jiejieTop 目前未适配Windows，您这边可以自己写一个platform

• Fixes platform 目录下找不到适配 windows 的文件 #45

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.