[Perf-training] Using os.devnull instead of a temp file

This is based on post-commit feedback from Vedant. Totally didn't know that existed and worked on Windows.

Thanks Vedant!

llvm-svn: 264064

clang/utils/perf-training/perf-helper.py

@@ -152,12 +152,9 @@ def cc1(args):
 
   # clear the profile file env, so that we don't generate profdata
   # when capturing the cc1 command
-  handle, profraw_file = tempfile.mkstemp()
-  os.close(handle)
   cc1_env = test_env
-  cc1_env["LLVM_PROFILE_FILE"] = profraw_file
+  cc1_env["LLVM_PROFILE_FILE"] = os.devnull
   cc1_cmd = get_cc1_command_for_args(cmd, cc1_env)
-  os.remove(profraw_file)
 
   subprocess.check_call(cc1_cmd)
   return 0;