Warn users whenever `python2` is invoked.

--- a/Modules/main.c
+++ b/Modules/main.c
@@ -237,6 +237,20 @@ static int RunMainFromImporter(char *filename)
     return -1;
 }
 
+void deprecate_warn(FILE *fp)
+{
+    int tty = isatty(2);
+    if (tty)
+        fprintf(fp, "\e[5;1;31m");
+    fprintf(fp, "%s: warning: Python 2.7 is deprecated and will be removed from CrOS by end of 2021. All users must migrate ASAP.\n",
+            orig_argv[0]);
+    fprintf(fp, "%s: commandline:", orig_argv[0]);
+    for (int i = 1; i < orig_argc; ++i)
+        fprintf(fp, " %s", orig_argv[i]);
+    if (tty)
+        fprintf(fp, "\e[m");
+    fprintf(fp, "\n");
+}
 
 /* Main program */
 
@@ -372,6 +372,7 @@ Py_Main(int argc, char **argv)
                 _Py_QnewFlag = 1;
                 break;
             }
+            deprecate_warn(stderr);
             fprintf(stderr,
                 "-Q option should be `-Qold', "
                 "`-Qwarn', `-Qwarnall', or `-Qnew' only\n");
@@ -458,14 +459,19 @@ Py_Main(int argc, char **argv)
         }
     }
 
-    if (help)
+    if (help) {
+        deprecate_warn(stderr);
         return usage(0, argv[0]);
+    }
 
     if (version) {
+        deprecate_warn(stdout);
         fprintf(stderr, "Python %s\n", PY_VERSION);
         return 0;
     }
 
+    deprecate_warn(stderr);
+
     if (Py_Py3kWarningFlag && !Py_TabcheckFlag)
         /* -3 implies -t (but not -tt) */
         Py_TabcheckFlag = 1;