I did some more testing, and the problem seems to arise with the fact that LLVM downloaded directly from the website, uses MSVC, causing problems with linking and the runtime. Though I am not so sure why SFML is being marked as MD_DynamicRelease when it is static libraries. I tried using clang from MinGW, which uses GCC's standard library and that seems to work fine. I am not sure if this is an issue with MSVC or SFML, but it most likely seems to be an MSVC issue