fix: wasm-bare targets compiling x86 builtins

Added sanity check to bootstrap to hard error on wasm builds without
clang, and changed distribution image `dist-various-2` to use clang to
build for official targets.

Author: JayAndJef

src/bootstrap/src/core/sanity.rs

@@ -314,6 +314,17 @@ than building it.
             .entry(*target)
             .or_insert_with(|| Target::from_triple(&target.triple));
 
+        // compiler-rt c fallbacks for wasm cannot be built with gcc
+        if target.contains("wasm") // bare metal targets without wasi sdk
+            && (build.config.optimized_compiler_builtins(*target)
+                || build.config.rust_std_features.contains("compiler-builtins-c"))
+        {
+            let is_clang = build.cc_tool(*target).is_like_clang();
+            if !is_clang {
+                panic!("only clang supports building c code for wasm targets");
+            }
+        }
+
         if (target.contains("-none-") || target.contains("nvptx"))
             && build.no_std(*target) == Some(false)
         {

src/bootstrap/src/lib.rs

@@ -27,6 +27,7 @@ use std::{env, fs, io, str};
 
 use build_helper::ci::gha;
 use build_helper::exit;
+use cc::Tool;
 use termcolor::{ColorChoice, StandardStream, WriteColor};
 use utils::build_stamp::BuildStamp;
 use utils::channel::GitInfo;
@@ -1198,6 +1199,11 @@ Executed at: {executed_at}"#,
         self.cc.borrow()[&target].path().into()
     }
 
+    /// Returns the internal `cc::Tool`
+    fn cc_tool(&self, target: TargetSelection) -> Tool {
+        self.cc.borrow()[&target].clone()
+    }
+
     /// Returns C flags that `cc-rs` thinks should be enabled for the
     /// specified target by default.
     fn cc_handled_clags(&self, target: TargetSelection, c: CLang) -> Vec<String> {

src/ci/docker/host-x86_64/dist-various-2/Dockerfile

@@ -65,6 +65,10 @@ ENV \
     CXX_i686_unknown_uefi=clang++-11 \
     CC_x86_64_unknown_uefi=clang-11 \
     CXX_x86_64_unknown_uefi=clang++-11 \
+    CC_wasm32_unknown_unknown=clang-11 \
+    CXX_wasm32_unknown_unknown=clang++-11 \
+    CC_wasm32v1_none=clang-11 \
+    CXX_wasm32v1_none=clang++-11 \
     CC=gcc-9 \
     CXX=g++-9
 

src/ci/docker/host-x86_64/test-various/Dockerfile

@@ -4,6 +4,7 @@ ARG DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends \
   clang-11 \
   llvm-11 \
+  gcc-multilib \
   g++ \
   make \
   ninja-build \
@@ -59,8 +60,8 @@ RUN curl -L https://github.com/bytecodealliance/wasmtime/releases/download/v19.0
   tar -xJ
 ENV PATH "$PATH:/wasmtime-v19.0.0-x86_64-linux"
 
-ENV WASM_TARGETS=wasm32-wasip1
-ENV WASM_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_TARGETS \
+ENV WASM_WASIP_TARGET=wasm32-wasip1 
+ENV WASM_WASIP_SCRIPT python3 /checkout/x.py --stage 2 test --host='' --target $WASM_WASIP_TARGET \
   tests/run-make \
   tests/ui \
   tests/mir-opt \
@@ -90,4 +91,4 @@ ENV UEFI_TARGETS=aarch64-unknown-uefi,i686-unknown-uefi,x86_64-unknown-uefi \
 ENV UEFI_SCRIPT python3 /checkout/x.py --stage 2 build --host='' --target $UEFI_TARGETS && \
   python3 -u /uefi_qemu_test/run.py
 
-ENV SCRIPT $WASM_SCRIPT && $NVPTX_SCRIPT && $MUSL_SCRIPT && $UEFI_SCRIPT
+ENV SCRIPT $WASM_WASIP_SCRIPT && $NVPTX_SCRIPT && $MUSL_SCRIPT && $UEFI_SCRIPT