Remove a couple of strerror() calls

Change to using %m in the error message string.  We need to be a bit
careful here to preserve errno until we need to print it.

This change avoids the use of not-thread-safe strerror() and unifies
some error message strings, and maybe makes the code appear more
consistent.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/daa87d79-c044-46c4-8458-8d77241ed7b0%40eisentraut.org

src/backend/libpq/hba.c

@@ -624,8 +624,11 @@ open_auth_file(const char *filename, int elevel, int depth,
 				 errmsg("could not open file \"%s\": %m",
 						filename)));
 		if (err_msg)
-			*err_msg = psprintf("could not open file \"%s\": %s",
+		{
-								filename, strerror(save_errno));
+			errno = save_errno;
+			*err_msg = psprintf("could not open file \"%s\": %m",
+								filename);
+		}
 		/* the caller may care about some specific errno */
 		errno = save_errno;
 		return NULL;
@@ -762,8 +765,9 @@ tokenize_auth_file(const char *filename, FILE *file, List **tok_lines,
 			ereport(elevel,
 					(errcode_for_file_access(),
 					 errmsg("could not read file \"%s\": %m", filename)));
-			err_msg = psprintf("could not read file \"%s\": %s",
+			errno = save_errno;
-							   filename, strerror(save_errno));
+			err_msg = psprintf("could not read file \"%s\": %m",
+							   filename);
 			break;
 		}