Fixed emscripten build

Hello I just fixed a few header-files blocking the build with emcc.
However, there is still an error that requires commenting out the `_LARGEFILE_64` defines in `emscripten/system/include/libc/stdio.h` I have not yet found a neat fix for that.
And one still needs `llvm-tblgen`, `clang-tblgen` and `llvm-config` form a _native build_