Can't find referenced headers

[ethindp]

Brief Description

When adding headers via Headers.Add, the headers referenced can't be found, but libraries are found just fine.

OS: NixOS 22.05, kernel v. 5.18.17

Used headers

synthizer.h and synthizer_constants.h.

Used settings

Target: GCC/Clang

Other settings

        options.OutputDir = "Synthizer";
        options.GeneratorKind = GeneratorKind.CSharp;
        options.Verbose = true;
        options.CompileCode = true;
        options.CheckSymbols = true;
        options.OutputInteropIncludes = true;
        options.GenerateFunctionTemplates = true;
        options.GenerateClassTemplates = true;
        options.GenerateInternalImports = true;
        options.GenerateSequentialLayout = true;
        options.UseHeaderDirectories = true;
        options.GenerateObjectOverrides = true;
        options.GenerateFinalizers = true;
        options.MarshalCharAsManagedChar = true;
        options.GenerateExternalDataFields = true;
        options.IncludePrefix = ".";

Stack trace or incompilable generated code

None generated.