Fixes to log output (remove "Formatter" lines, fix order)

 * Prefix "clang-format" to the Excluding lines rather than print
   "Formatter darker (Python code formatter):" and
   "Formatter clang-format (C/C++ code formatter):" Those formatter
   lines were being printed even when there were no C++/Python files to
   format.

 * Capture stderr and then print it out, rather than let the subprocess
   directly write it out. This ensures that output appears in the right
   order when the script's output is buffered.

Author: rprichard

llvm/utils/git/code-format-helper.py

@@ -86,7 +86,6 @@ def update_pr(
             pr.as_issue().create_comment(comment_text)
 
     def run(self, changed_files: list[str], args: argparse.Namespace) -> bool:
-        print(f"Formatter {self.name} ({self.friendly_name}):")
         diff = self.format_run(changed_files, args)
         if diff is None:
             comment_text = f"""
@@ -123,7 +122,7 @@ def libcxx_excluded_files(self) -> list[str]:
 
     def should_be_excluded(self, path: str) -> bool:
         if path in self.libcxx_excluded_files:
-            print(f"Excluding file {path}")
+            print(f"{self.name}: Excluding file {path}")
             return True
         return False
 
@@ -151,7 +150,8 @@ def format_run(
         ] + cpp_files
         print(f"Running: {' '.join(cf_cmd)}")
         self.cf_cmd = cf_cmd
-        proc = subprocess.run(cf_cmd, stdout=subprocess.PIPE)
+        proc = subprocess.run(cf_cmd, capture_output=True)
+        sys.stdout.write(proc.stderr.decode("utf-8"))
 
         if proc.returncode != 0:
             # formatting needed, or the command otherwise failed
@@ -194,7 +194,8 @@ def format_run(
         ] + py_files
         print(f"Running: {' '.join(darker_cmd)}")
         self.darker_cmd = darker_cmd
-        proc = subprocess.run(darker_cmd, stdout=subprocess.PIPE)
+        proc = subprocess.run(darker_cmd, capture_output=True)
+        sys.stdout.write(proc.stderr.decode("utf-8"))
 
         if proc.returncode != 0:
             # formatting needed, or the command otherwise failed