--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,32 @@
+2010-11-20  Bruno Haible  <bruno@clisp.org>
+
+	Ensure that <features.h> is included before __GLIBC__ is tested.
+	* lib/printf-parse.h: Include <features.h>.
+	* m4/vasnprintf.m4 (gl_PREREQ_PRINTF_PARSE): Require gl_FEATURES_H.
+	Reported by Mike Frysinger <vapier@gentoo.org>.
+
+	Ensure that <features.h> is included before __GLIBC__ is tested.
+	* lib/wchar.in.h: Include <features.h>.
+	* m4/wchar_h.m4 (gl_WCHAR_H): Require gl_FEATURES_H.
+	* modules/wchar (Makefile.am): Substitute HAVE_FEATURES_H.
+	Reported by Mike Frysinger <vapier@gentoo.org>.
+
+	Ensure that <features.h> is included before __GLIBC__ is tested.
+	* lib/arpa_inet.in.h: Include <features.h>.
+	* m4/arpa_inet_h.m4 (gl_HEADER_ARPA_INET): Require gl_FEATURES_H.
+	* modules/arpa_inet (Makefile.am): Substitute HAVE_FEATURES_H.
+	Reported by Mike Frysinger <vapier@gentoo.org>.
+
+	Ensure that <features.h> is included before __GLIBC__ is tested.
+	* build-aux/link-warning.h: Include <features.h>.
+	* modules/link-warning (configure.ac): Require gl_FEATURES_H.
+	(Makefile.am): Substitute HAVE_FEATURES_H into link-warning.h.
+	Reported by Mike Frysinger <vapier@gentoo.org>.
+
+	Ensure that <features.h> is included before __GLIBC__ is tested.
+	* m4/gnulib-common.m4 (gl_FEATURES_H): New macro.
+	Reported by Mike Frysinger <vapier@gentoo.org>.
+
 2010-11-20  Bruno Haible  <bruno@clisp.org>
 
 	memmem: Fix autoconf test.

--- a/build-aux/link-warning.h
+++ b/build-aux/link-warning.h
@@ -15,6 +15,10 @@
    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#if @HAVE_FEATURES_H@
+# include <features.h> /* for __GLIBC__, __UCLIBC__ */
+#endif
+
 /* GL_LINK_WARNING("literal string") arranges to emit the literal string as
    a linker warning on most glibc systems.
    We use a linker warning rather than a preprocessor warning, because

--- a/lib/arpa_inet.in.h
+++ b/lib/arpa_inet.in.h
@@ -23,6 +23,10 @@
 #endif
 @PRAGMA_COLUMNS@
 
+#if @HAVE_FEATURES_H@
+# include <features.h> /* for __GLIBC__ */
+#endif
+
 /* Gnulib's sys/socket.h is responsible for pulling in winsock2.h etc
    under MinGW.
    But avoid namespace pollution on glibc systems.  */

--- a/lib/printf-parse.h
+++ b/lib/printf-parse.h
@@ -23,6 +23,10 @@
      ENABLE_UNISTDIO    Set to 1 to enable the unistdio extensions.
      STATIC             Set to 'static' to declare the function static.  */
 
+#if HAVE_FEATURES_H
+# include <features.h> /* for __GLIBC__, __UCLIBC__ */
+#endif
+
 #include "printf-args.h"
 
 

--- a/lib/wchar.in.h
+++ b/lib/wchar.in.h
@@ -53,6 +53,10 @@
 
 #define _GL_ALREADY_INCLUDING_WCHAR_H
 
+#if @HAVE_FEATURES_H@
+# include <features.h> /* for __GLIBC__ */
+#endif
+
 /* Tru64 with Desktop Toolkit C has a bug: <stdio.h> must be included before
    <wchar.h>.
    BSD/OS 4.0.1 has a bug: <stddef.h>, <stdio.h> and <time.h> must be

--- a/m4/arpa_inet_h.m4
+++ b/m4/arpa_inet_h.m4
@@ -1,4 +1,4 @@
-# arpa_inet_h.m4 serial 9
+# arpa_inet_h.m4 serial 10
 dnl Copyright (C) 2006, 2008-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -22,6 +22,8 @@
   dnl <arpa/inet.h> is always overridden, because of GNULIB_POSIXCHECK.
   gl_CHECK_NEXT_HEADERS([arpa/inet.h])
 
+  AC_REQUIRE([gl_FEATURES_H])
+
   dnl Check for declarations of anything we want to poison if the
   dnl corresponding gnulib module is not in use.
   gl_WARN_ON_USE_PREPARE([[

--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 20
+# gnulib-common.m4 serial 21
 dnl Copyright (C) 2007-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -102,6 +102,19 @@
     [Define to 1 when the gnulib module $1 should be tested.])
 ])
 
+# Test whether <features.h> exists.
+# Set HAVE_FEATURES_H.
+AC_DEFUN([gl_FEATURES_H],
+[
+  AC_CHECK_HEADERS_ONCE([features.h])
+  if test $ac_cv_header_features_h = yes; then
+    HAVE_FEATURES_H=1
+  else
+    HAVE_FEATURES_H=0
+  fi
+  AC_SUBST([HAVE_FEATURES_H])
+])
+
 # m4_foreach_w
 # is a backport of autoconf-2.59c's m4_foreach_w.
 # Remove this macro when we can assume autoconf >= 2.60.

--- a/m4/vasnprintf.m4
+++ b/m4/vasnprintf.m4
@@ -1,4 +1,4 @@
-# vasnprintf.m4 serial 31
+# vasnprintf.m4 serial 32
 dnl Copyright (C) 2002-2004, 2006-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -40,6 +40,7 @@
 # Prequisites of lib/printf-parse.h, lib/printf-parse.c.
 AC_DEFUN([gl_PREREQ_PRINTF_PARSE],
 [
+  AC_REQUIRE([gl_FEATURES_H])
   AC_REQUIRE([AC_TYPE_LONG_LONG_INT])
   AC_REQUIRE([gt_TYPE_WCHAR_T])
   AC_REQUIRE([gt_TYPE_WINT_T])

--- a/m4/wchar_h.m4
+++ b/m4/wchar_h.m4
@@ -7,7 +7,7 @@
 
 dnl Written by Eric Blake.
 
-# wchar_h.m4 serial 34
+# wchar_h.m4 serial 35
 
 AC_DEFUN([gl_WCHAR_H],
 [
@@ -26,6 +26,8 @@
   fi
   AC_SUBST([HAVE_WCHAR_H])
 
+  AC_REQUIRE([gl_FEATURES_H])
+
   AC_REQUIRE([gt_TYPE_WINT_T])
   if test $gt_cv_c_wint_t = yes; then
     HAVE_WINT_T=1

--- a/modules/arpa_inet
+++ b/modules/arpa_inet
@@ -27,6 +27,7 @@
 	  sed -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
 	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
 	      -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
+	      -e 's|@''HAVE_FEATURES_H''@|$(HAVE_FEATURES_H)|g' \
 	      -e 's|@''NEXT_ARPA_INET_H''@|$(NEXT_ARPA_INET_H)|g' \
 	      -e 's|@''HAVE_ARPA_INET_H''@|$(HAVE_ARPA_INET_H)|g' \
 	      -e 's|@''GNULIB_INET_NTOP''@|$(GNULIB_INET_NTOP)|g' \

--- a/modules/link-warning
+++ b/modules/link-warning
@@ -10,6 +10,7 @@
 Depends-on:
 
 configure.ac:
+AC_REQUIRE([gl_FEATURES_H])
 
 Makefile.am:
 # The BUILT_SOURCES created by this Makefile snippet are not used via #include
@@ -22,8 +23,9 @@
 # build-aux/link-warning.h, except that it has the copyright header cut off.
 link-warning.h: $(top_srcdir)/build-aux/link-warning.h
 	$(AM_V_GEN)rm -f $@-t $@ && \
-	sed -n -e '/GL_LINK_WARNING/,$$p' \
+	sed -n -e '/HAVE_FEATURES_H/,$$p' \
 	  < $(top_srcdir)/build-aux/link-warning.h \
+	| sed -e 's|@''HAVE_FEATURES_H''@|$(HAVE_FEATURES_H)|g' \
 	  > $@-t && \
 	mv $@-t $@
 MOSTLYCLEANFILES += link-warning.h link-warning.h-t

--- a/modules/wchar
+++ b/modules/wchar
@@ -27,6 +27,7 @@
 	  sed -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
 	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
 	      -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
+	      -e 's|@''HAVE_FEATURES_H''@|$(HAVE_FEATURES_H)|g' \
 	      -e 's|@''NEXT_WCHAR_H''@|$(NEXT_WCHAR_H)|g' \
 	      -e 's|@''HAVE_WCHAR_H''@|$(HAVE_WCHAR_H)|g' \
 	      -e 's|@''GNULIB_BTOWC''@|$(GNULIB_BTOWC)|g' \