Fix jemalloc builds for Windows MSVC targets

[han1548772930]

## Summary

This PR fixes building `tikv-jemalloc-sys` for Windows MSVC targets.

## Changes

- Maps Windows MSVC targets to Autoconf-compatible target triples.
- Links the correct `jemalloc_s.lib` library on Windows.
- Preserves the build directory until the final Rust linking step.
- Adds the correct native library search path.

## Building on Windows

Requirements:

- Rust MSVC toolchain
- Visual Studio with the **Desktop development with C++** workload
- MSYS2 with `mingw32-make`

Open the Visual Studio x64 developer command prompt, then add the MSYS2
`ucrt64/bin` and `usr/bin` directories to `PATH`.

Verify the required tools:

```bat
where cl.exe
where lib.exe
where link.exe
where sh.exe
where mingw32-make.exe

Then build:

cargo build

For jemalloc profiling:

tikv-jemallocator = { version = "0.7.0", features = ["profiling"] }

Tested with the x86_64-pc-windows-msvc Rust target.

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

* **Bug Fixes**
  * Improved Windows builds by correctly preserving build output and linking the appropriate library.
  * Updated Windows target handling to improve compatibility with supported toolchains.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

[ti-chi-bot]

Welcome @han1548772930! It looks like this is your first PR to tikv/jemallocator 🎉

[coderabbitai]

📝 Walkthrough

Walkthrough

The build script now uses Windows-specific target mappings, preserves Windows build output directories, and emits platform-specific linker names and search paths.

Changes

Windows jemalloc build handling

Layer / File(s)	Summary
Windows GNU target mapping jemalloc-sys/build.rs	MSVC Windows targets now map to mingw32 variants instead of win32.
Platform-specific artifact linking jemalloc-sys/build.rs	Windows retains the build directory and links jemalloc_s from its lib directory; non-Windows builds remove it and link jemalloc_pic from OUT_DIR/lib.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely matches the main change: fixing jemalloc builds for Windows MSVC targets.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

Thanks for your pull request. Before we can look at it, you'll need to add a 'DCO signoff' to your commits.

📝 Please follow instructions in the contributing guide to update your commits with the DCO

Full details of the Developer Certificate of Origin can be found at developercertificate.org.

The list of commits missing DCO signoff:

• 4a0b928 fix Windows MSVC jemalloc target triple
• 40226a3 fix MSVC static jemalloc library linkage

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