Fix linking stdc++ on wasi

Author: bjorn3

config.llvm.toml

@@ -35,6 +35,8 @@ sysconfdir = "etc"
 [target.'wasm32-wasip1-threads']
 wasi-root = "wasi-sdk-24.0-x86_64-linux/share/wasi-sysroot"
 # codegen-backends = ["cranelift"]
+cc = "/home/bjorn/Projects/rust/wasi-sdk-24.0-x86_64-linux/bin/clang"
+cxx = "/home/bjorn/Projects/rust/wasi-sdk-24.0-x86_64-linux/bin/clang"
 linker = "wasi-sdk-24.0-x86_64-linux/bin/clang"
 codegen-backends = ["llvm"]
 

src/bootstrap/src/core/build_steps/compile.rs

@@ -1253,7 +1253,9 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
 
     // Building with a static libstdc++ is only supported on linux right now,
     // not for MSVC or macOS
-    if builder.config.llvm_static_stdcpp
+    if target.contains("wasi") {
+        cargo.env("LLVM_STATIC_STDCPP", builder.wasi_libdir(target).unwrap().join("libstdc++.a"));
+    } else if builder.config.llvm_static_stdcpp
         && !target.contains("freebsd")
         && !target.is_msvc()
         && !target.contains("apple")