With the current release of emscripten it's impossible to build even the simplest example:

```
$ emcc --clear-cache
emcc:INFO: clearing cache as requested by --clear-cache
shared:INFO: (Emscripten: Running sanity checks)

$ emcc hello_world.c
cache:INFO: generating system asset: is_vanilla.txt... (this will be cached in "/home/raul/.cache/emscripten/cache/is_vanilla.txt" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libcompiler_rt.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libcompiler_rt.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc-wasm.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libc-wasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++-noexcept.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libc++-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++abi-noexcept.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libc++abi-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libdlmalloc.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libdlmalloc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libpthread_stub.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libpthread_stub.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc_rt_wasm.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libc_rt_wasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libsockets.a... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/libsockets.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system asset: generated_struct_info.json... (this will be cached in "/home/raul/.cache/emscripten/cache/wasm/generated_struct_info.json" for subsequent builds)
Fatal: Module::addExport: stackSave already exists
emcc: error: '/usr/bin/wasm-emscripten-finalize --detect-features --global-base=1024 --check-stack-overflow /tmp/emscripten_temp_f2v4qpcj/tmpsbxi86li.wasm -o /tmp/emscripten_temp_f2v4qpcj/tmpsbxi86li.wasm.o.wasm' failed (1)
FAIL: Compilation failed!: ['/usr/lib/emscripten/emcc', '-D_GNU_SOURCE', '-o', '/tmp/tmpsbxi86li.js', '/tmp/tmpu3qgyz2y.c', '-O0', '--js-opts', '0', '--memory-init-file', '0', '-Werror', '-Wno-format', '-s', 'BOOTSTRAPPING_STRUCT_INFO=1', '-s', 'WARN_ON_UNDEFINED_SYMBOLS=0', '-s', 'STRICT=1', '-s', 'SINGLE_FILE=1']
```

This is because emscripten added support for the builtin stack functions:
- https://github.com/emscripten-core/emscripten/pull/11166

Binaryen adapted to the change in: https://github.com/WebAssembly/binaryen/pull/2852

But it's unreleased. Building binaryen master/HEAD fixes the issue.