Update gnulib to 8f4538a53d64054ae2fc8b86c0f87c418c6176e6

Includes gnulib:0c907f7da13232908f05c415b8cec56024071906 to fix #49930
https://lists.gnu.org/archive/html/bug-guile/2021-08/msg00003.html.

lib/math.c

@@ -1,4 +1,22 @@
+/* Inline functions for <math.h>.
+
+   Copyright (C) 2012-2021 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
 #include <config.h>
+
 #define _GL_MATH_INLINE _GL_EXTERN_INLINE
 #include "math.h"
 typedef int dummy;