emit old upstream warning no matter the build step

src/bootstrap/src/core/build_steps/format.rs

@@ -7,7 +7,7 @@ use std::sync::mpsc::SyncSender;
 use std::sync::Mutex;
 
 use build_helper::ci::CiEnv;
-use build_helper::git::{get_git_modified_files, warn_old_master_branch};
+use build_helper::git::get_git_modified_files;
 use ignore::WalkBuilder;
 
 use crate::core::builder::Builder;
@@ -93,8 +93,6 @@ fn get_modified_rs_files(build: &Builder<'_>) -> Result<Option<Vec<String>>, Str
     if !verify_rustfmt_version(build) {
         return Ok(None);
     }
-    warn_old_master_branch(&build.config.git_config(), &build.config.src)
-        .map_err(|e| e.to_string())?;
     get_git_modified_files(&build.config.git_config(), Some(&build.config.src), &["rs"])
 }
 

src/bootstrap/src/core/sanity.rs

@@ -15,6 +15,8 @@ use std::ffi::{OsStr, OsString};
 use std::path::PathBuf;
 use std::{env, fs};
 
+use build_helper::git::warn_old_master_branch;
+
 #[cfg(not(feature = "bootstrap-self-test"))]
 use crate::builder::Builder;
 use crate::builder::Kind;
@@ -379,4 +381,8 @@ $ pacman -R cmake && pacman -S mingw-w64-x86_64-cmake
     if let Some(ref s) = build.config.ccache {
         cmd_finder.must_have(s);
     }
+
+    warn_old_master_branch(&build.config.git_config(), &build.config.src)
+        .map_err(|e| e.to_string())
+        .unwrap();
 }