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This patch is part of a series to support driver managed module builds for C++ named modules and Clang modules. This introduces a scanner that detects C++ named module usage early in the driver with only negligible overhead. For now, it is enabled only with the `-fmodules-driver` flag and serves solely diagnostic purposes. In the future, the scanner will be enabled for any (modules-driver compatible) compilation with two or more inputs, and will help the driver determine whether to implicitly enable the modules driver. Since the scanner adds very little overhead, we are also exploring enabling it for compilations with only a single input. This approach could allow us to detect `import std` usage in a single-file compilation, which would then activate the modules driver. For performance measurements on this, see https://github.com/naveen-seth/llvm-dev-cxx-modules-check-benchmark. RFC for driver managed module builds: https://discourse.llvm.org/t/rfc-modules-support-simple-c-20-modules-use-from-the-clang-driver-without-a-build-system This patch relands the reland (2d31fc8) for commit ded1426. The earlier reland failed due to a missing link dependency on `clangLex`. This reland fixes the issue by adding the link dependency after discussing it in the following RFC: https://discourse.llvm.org/t/rfc-driver-link-the-driver-against-clangdependencyscanning-clangast-clangfrontend-clangserialization-and-clanglex