Avoid non-constant format string argument to fprintf().

As Tom Lane pointed out, it could defeat the compiler's printf() format
string verification.

Backpatch to v12, like that patch that introduced it.

Discussion: https://www.postgresql.org/message-id/1069283.1597672779%40sss.pgh.pa.us

src/bin/pg_basebackup/pg_basebackup.c

@@ -860,7 +860,7 @@ progress_report(int tablespacenum, const char *filename,
 	 * Stay on the same line if reporting to a terminal and we're not done
 	 * yet.
 	 */
-	fprintf(stderr, (!finished && isatty(fileno(stderr))) ? "\r" : "\n");
+	fputc((!finished && isatty(fileno(stderr))) ? '\r' : '\n', stderr);
 }
 
 static int32

src/bin/pg_checksums/pg_checksums.c

@@ -166,7 +166,7 @@ progress_report(bool finished)
 	 * Stay on the same line if reporting to a terminal and we're not done
 	 * yet.
 	 */
-	fprintf(stderr, (!finished && isatty(fileno(stderr))) ? "\r" : "\n");
+	fputc((!finished && isatty(fileno(stderr))) ? '\r' : '\n', stderr);
 }
 
 static bool

src/bin/pg_rewind/pg_rewind.c

@@ -572,7 +572,7 @@ progress_report(bool finished)
 	 * Stay on the same line if reporting to a terminal and we're not done
 	 * yet.
 	 */
-	fprintf(stderr, (!finished && isatty(fileno(stderr))) ? "\r" : "\n");
+	fputc((!finished && isatty(fileno(stderr))) ? '\r' : '\n', stderr);
 }
 
 /*