compiletest: let config flags overwrite -A unused

Author: RalfJung

src/tools/compiletest/src/runtest.rs

@@ -1958,6 +1958,12 @@ impl<'test> TestCx<'test> {
             None => {}
         }
 
+        // Add `-A unused` before `config` flags and in-test (`props`) flags, so that they can
+        // overwrite this.
+        if let AllowUnused::Yes = allow_unused {
+            rustc.args(&["-A", "unused"]);
+        }
+
         if self.props.force_host {
             self.maybe_add_external_args(
                 &mut rustc,
@@ -1980,10 +1986,6 @@ impl<'test> TestCx<'test> {
             rustc.arg("-Ctarget-feature=-crt-static");
         }
 
-        if let AllowUnused::Yes = allow_unused {
-            rustc.args(&["-A", "unused"]);
-        }
-
         rustc.args(&self.props.compile_flags);
 
         rustc