Fix cross compilation testing

Author: oli-obk

tests/pass/random.rs

@@ -1,4 +1,6 @@
 use rand::{rngs::SmallRng, Rng, SeedableRng};
+// mac-os `rand` does some pointer shenanigans
+//@compile-flags: -Zmiri-permissive-provenance
 
 fn main() {
     // Test `getrandom` directly (in multiple different versions).

ui_test/src/dependencies.rs

@@ -32,15 +32,16 @@ pub fn build_dependencies(config: &Config) -> Result<Dependencies> {
     // support `cargo miri build` yet.
     build.arg("run");
 
+    if let Some(target) = &config.target {
+        build.arg(format!("--target={target}"));
+    }
+
     // Reusable closure for setting up the environment both for artifact generation and `cargo_metadata`
     let setup_command = |cmd: &mut Command| {
         // Avoid poisoning the target directory and causing unnecessary rebuilds.
         cmd.env_remove("RUSTFLAGS");
 
         cmd.envs(envs.iter().map(|(k, v)| (k, v)));
-        if let Some(target) = &config.target {
-            cmd.arg(format!("--target={target}"));
-        }
         cmd.arg("--manifest-path").arg(manifest_path);
     };