identifier "size_t" is undefined, with clang 18

[Colengms]

With clang 18(.1.3), I'm seeing an issue with size_t, which doesn't repro with earlier versions of clang. (15-17).

The issue likely has something to do with how the clang-18 headers decide whether or not to define size_t. Some IntelliSense predefines may be confusing it, making it think size_t is already defined.

[sfan5]

Can confirm this with Clang 18.1.8 and vscode-cpptools 1.22.0 on Linux x64.
I have the settings automatically detected from compile_commands.json, which always used to work fine.

[browntarik]

I have filed a bug with the internal VS (2253203) Team. As this is most likely the cause of #12319, that bug will be put on the back burner until this has been resolved.

[bobbrow]

A workaround is to add this to your defines in c_cpp_properties.json:

    "defines": [
        "__building_module(x)=0"
    ]

I don't know that we have an easy way to inject that in the compile_commands.json case, but someone else on the team may have an idea.