build: Allow building C compiler-rt fallbacks for wasm

.github/workflows/main.yml

@@ -90,8 +90,8 @@ jobs:
     - run: rustup component add llvm-tools-preview
     - name: Download compiler-rt reference sources
       run: |
-        curl -L -o code.tar.gz https://github.com/rust-lang/llvm-project/archive/rustc/12.0-2021-04-15.tar.gz
-        tar xzf code.tar.gz --strip-components 1 llvm-project-rustc-12.0-2021-04-15/compiler-rt
+        curl -L -o code.tar.gz https://github.com/rust-lang/llvm-project/archive/rustc/13.0-2021-08-08.tar.gz
+        tar xzf code.tar.gz --strip-components 1 llvm-project-rustc-13.0-2021-08-08/compiler-rt
         echo RUST_COMPILER_RT_ROOT=./compiler-rt >> $GITHUB_ENV
       shell: bash
 

build.rs

@@ -56,10 +56,8 @@ fn main() {
     if !cfg!(feature = "mangled-names") && cfg!(feature = "c") {
         // Don't use a C compiler for these targets:
         //
-        // * wasm - clang for wasm is somewhat hard to come by and it's
-        //   unlikely that the C is really that much better than our own Rust.
         // * nvptx - everything is bitcode, not compatible with mixed C/Rust
-        if !target.contains("wasm") && !target.contains("nvptx") {
+        if !target.contains("nvptx") {
             #[cfg(feature = "c")]
             c::compile(&llvm_target, &target);
         }

ci/docker/wasm32-unknown-unknown/Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:20.04
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-    gcc libc6-dev ca-certificates
+    gcc clang libc6-dev ca-certificates
 
 ENV CARGO_TARGET_WASM32_UNKNOWN_UNKNOWN_RUNNER=true

ci/run.sh

@@ -66,6 +66,7 @@ for rlib in $(echo $path); do
       grep -v __x86.get_pc_thunk | \
       grep -v __builtin_cl | \
       grep -v __builtin_ctz | \
+      grep -v __builtin_sadd_overflow | \
       grep 'T __'
 
     if test $? = 0; then