common: json.h: fix clang lto

[ngxson]

Overview

Ref discussion #27511

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: yes

[maddes8cht]

As requested in #27511 (comment) I've compiled this PR under windows.

Tested and confirmed working! ✅

I encountered the LTO linking issue on Windows with clang-cl + -flto=thin, and this PR resolves it for me.

Test environment:

• Windows 11
• AMD Ryzen 5 3600X (6 cores, 12 threads)
• NVIDIA RTX 3060 (12GB VRAM)
• clang-cl (LLVM) with ThinLTO enabled
• Static linking with vcpkg (x64-windows-static)

Build flags:

-DCMAKE_C_COMPILER=clang-cl
-DCMAKE_CXX_COMPILER=clang-cl
-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON
-DCMAKE_CXX_FLAGS="/EHsc /O2 /D_CRT_SECURE_NO_WARNINGS /wd4996 /D_AMD64_ -flto=thin"
-DCMAKE_C_FLAGS="/EHsc /O2 /D_CRT_SECURE_NO_WARNINGS /wd4996 /D_AMD64_ -flto=thin"
-DGGML_LTO=ON

Results:

• Build completes successfully
• binaries (tested llama.exe, llama-cli.exe, llama-server.exe) execute normally

Thank you for the fix!