web-wasm: Migrate to Emscripten LLVM upstream backend, 1.39.18
web-wasm: Migrate to Emscripten LLVM upstream backend, 1.39.18

thewtex/cross-compilers,dockcross/dockcross,thewtex/cross-compilers,dockcross/dockcross,thewtex/cross-compilers,dockcross/dockcross,dockcross/dockcross,thewtex/cross-compilers