allow failure on proc-macro crate check

Signed-off-by: onur-ozkan <work@onurozkan.dev>

src/bootstrap/src/core/builder/cargo.rs

@@ -654,6 +654,7 @@ impl Builder<'_> {
                 // supported by the target.
                 if target != compiler.host && cmd_kind != Kind::Check {
                     let error = command(self.rustc(compiler))
+                        .allow_failure()
                         .arg("--target")
                         .arg(target.rustc_target_arg())
                         .arg("--print=file-names")