Update gnulib to 8f4538a53d64054ae2fc8b86c0f87c418c6176e6

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

lib/libc-config.h

@@ -28,7 +28,10 @@
 
    When compiled as part of glibc this is a no-op; when compiled as
    part of Gnulib this includes Gnulib's <config.h> and defines macros
-   that glibc library code would normally assume.  */
+   that glibc library code would normally assume.
+
+   Note: This header file MUST NOT be included by public header files
+   of Gnulib.  */
 
 #include <config.h>
 
@@ -71,7 +74,7 @@
 # endif
 #endif
 
-#ifndef __attribute_maybe_unused__
+#ifndef __attribute_nonnull__
 /* <sys/cdefs.h> either does not exist, or is too old for Gnulib.
    Prepare to include <cdefs.h>, which is Gnulib's version of a
    more-recent glibc <sys/cdefs.h>.  */
@@ -80,13 +83,9 @@
 # ifndef _FEATURES_H
 #  define _FEATURES_H 1
 # endif
-/* Define __WORDSIZE so that <cdefs.h> does not attempt to include
-   nonexistent files.  Make it a syntax error, since Gnulib does not
-   use __WORDSIZE now, and if Gnulib uses it later the syntax error
-   will let us know that __WORDSIZE needs configuring.  */
-# ifndef __WORDSIZE
-#  define __WORDSIZE %%%
-# endif
+/* Define __GNULIB_CDEFS so that <cdefs.h> does not attempt to include
+   nonexistent files.  */
+# define __GNULIB_CDEFS
 /* Undef the macros unconditionally defined by our copy of glibc
    <sys/cdefs.h>, so that they do not clash with any system-defined
    versions.  */
@@ -118,6 +117,9 @@
 # undef __THROW
 # undef __THROWNL
 # undef __attr_access
+# undef __attr_access_none
+# undef __attr_dealloc
+# undef __attr_dealloc_free
 # undef __attribute__
 # undef __attribute_alloc_size__
 # undef __attribute_artificial__