Clippy: skip check_host_compiler check in rustc testsuite

This test only makes sense to run in the Clippy repo

In the Rust repo the name of the host_compiler is dev, not nightly

src/tools/clippy/tests/versioncheck.rs

@@ -93,6 +93,11 @@ fn check_that_clippy_has_the_same_major_version_as_rustc() {
 
 #[test]
 fn check_host_compiler() {
+    // do not run this test inside the upstream rustc repo:
+    if option_env!("RUSTC_TEST_SUITE").is_some() {
+        return;
+    }
+
     let version = rustc_tools_util::get_version_info!();
     assert_eq!(version.host_compiler, Some("nightly".to_string()));
 }