[clangd] Silence warning when compiling with MSVC targetting x86

This fixes:
```
[5240/6995] Building CXX object tools\clang\tools\extra\clangd\CMakeFiles\obj.clangDaemon.dir\InlayHints.cpp.obj
C:\git\llvm-project\clang-tools-extra\clangd\InlayHints.cpp(1098): warning C4018: '<': signed/unsigned mismatch
```