This directory contains stubs for SerenityOS libraries (LibC, LibM, LibDl, LibPthread) that are referenced from the LLVM runtime libraries. These are needed by the linker in order to add the required DT_NEEDED entries.

Generally, no. LLVM does not use the header files to decide which functionality it can use. After adding a new function to a header, you don't have to worry about LLVM toolchain builds failing because the symbol is not present in the stubs.

First, you need to have a working SerenityOS installation that's been built by the Clang toolchain. Then, using the llvm-ifs tool, these libraries need to be converted into a stripped-down stub form. To do that, run the following command:

Toolchain/Local/clang/bin/llvm-ifs --output-format=ELF --output=<path-to-stub> <path-to-original>