Give an error when attempting to build for MSVC

Author: bjorn3

y.rs

@@ -127,6 +127,14 @@ fn main() {
         host_triple.clone()
     };
 
+    if target_triple.ends_with("-msvc") {
+        eprintln!("The MSVC toolchain is not yet supported by rustc_codegen_cranelift.");
+        eprintln!("Switch to the MinGW toolchain for Windows support.");
+        eprintln!("Hint: You can use `rustup set default-host x86_64-pc-windows-gnu` to");
+        eprintln!("set the global default target to MinGW");
+        process::exit(1);
+    }
+
     let cg_clif_dylib = build_backend::build_backend(channel);
     build_sysroot::build_sysroot(
         channel,