[LLVMSupport] module static link zstd error.

In the released precompiled file “clang+llvm-23.1.1-x86_64-pc-windows-msvc.tar.zst,” the “LLVMSupport” module statically links the zstd library, but it still requires the user to provide the zstd library, which must be statically linked. This results in duplicate symbol definitions, and when using the MSVC compiler, the following error messages is displayed:
```bash
LINK: warning LNK4098: The default library “MSVCRT” conflicts with other libraries; please use /NODEFAULTLIB:library [E:\test\test_clang_ast\build\my_tool.vcxproj]
LINK : warning LNK4217: The symbol “calloc” (defined in “LLVMSupport.lib(rpmalloc.c.obj)”) has already been defined by “zstd_static.lib(zstd_compress.obj)” (in the function “ZSTD_createCCtxParams”
```

Start by reproducing the link failure with clang+llvm-23.1.1-x86_64-pc-windows-msvc.tar.zst, LLVMSupport.lib, and zstd_static.lib under MSVC. Read the LLVMSupport packaging and static-link configuration to determine why zstd is both included and required from the user. Done means the duplicate-symbol and MSVCRT warnings no longer occur for this usage.

Written by the indexing model from the issue text.