Re-enable wasm32-unknown-emscripten target.

Uses a trick described in
rust-lang/rust/issues#85821#issuecomment-969369677. Note that this still
allows it to run, despite there seemingly being no entry point: this has
no effect on the resulting code.

Related to #609. Partially fixes #839.

Author: Alexhuszagh

.github/workflows/ci.yml

@@ -182,9 +182,9 @@ jobs:
             - { target: x86_64-linux-android,             os: ubuntu-latest,  cpp: 1,           std: 1, run: 1, runners: qemu-user }
             - { target: x86_64-pc-windows-gnu,            os: ubuntu-latest,  cpp: 1,           std: 1, run: 1 }
             - { target: i686-pc-windows-gnu,              os: ubuntu-latest,  cpp: 1,           std: 1, run: 1 }
-            # Disabled for now, see https://github.com/rust-lang/rust/issues/85821
+            # Disabled for now, see https://github.com/rust-lang/rust/issues/98216
             #- { target: asmjs-unknown-emscripten,         os: ubuntu-latest,  cpp: 1,           std: 1, run: 1 }
-            #- { target: wasm32-unknown-emscripten,        os: ubuntu-latest,  cpp: 1,           std: 1, run: 1 }
+            - { target: wasm32-unknown-emscripten,        os: ubuntu-latest,  cpp: 1,           std: 1, run: 1 }
             - { target: x86_64-unknown-dragonfly,         os: ubuntu-latest,  cpp: 1, dylib: 1, std: 1, build-std: 1 }
             - { target: i686-unknown-freebsd,             os: ubuntu-latest,          dylib: 1, std: 1 }
             - { target: x86_64-unknown-freebsd,           os: ubuntu-latest,          dylib: 1, std: 1 }

docker/Dockerfile.wasm32-unknown-emscripten

@@ -16,4 +16,5 @@ RUN apt-get update && apt-get install --assume-yes --no-install-recommends \
   python
 
 ENV CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER=node \
-  BINDGEN_EXTRA_CLANG_ARGS_wasm32_unknown_emscripten="--sysroot=/emsdk/upstream/emscripten/cache/sysroot"
+  BINDGEN_EXTRA_CLANG_ARGS_wasm32_unknown_emscripten="--sysroot=/emsdk/upstream/emscripten/cache/sysroot" \
+  EMCC_CFLAGS="-s ERROR_ON_UNDEFINED_SYMBOLS=0 --no-entry ${EMCC_CFLAGS}"