This commit introduces support for running clang-repl and executing C++
code interactively inside a Javascript engine using WebAssembly when
built with Emscripten. This is achieved by producing WASM "shared
libraries" that can be loaded by the Emscripten runtime using dlopen()
More discussion is available in https://reviews.llvm.org/D158140
Co-authored-by: Anubhab Ghosh <anubhabghosh.me@gmail.com>
