Don't require GNU putenv

* configure.ac: Use system putenv even if it lacks GNU features, as
we don't need them.  This works around a bug in FreeBSD 10.1 getenv.
Fixes: bug#19874

ChangeLog

+2015-02-27  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Don't require GNU putenv
+	* configure.ac: Use system putenv even if it lacks GNU features, as
+	we don't need them.  This works around a bug in FreeBSD 10.1 getenv.
+	Fixes: bug#19874
+
 2015-02-25  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Merge from gnulib

configure.ac

@@ -780,6 +780,11 @@ AC_DEFUN([gl_CRYPTO_CHECK])
 # Avoid gnulib's tests for HAVE_WORKING_O_NOATIME and HAVE_WORKING_O_NOFOLLOW,
 # as we don't use them.
 AC_DEFUN([gl_FCNTL_O_FLAGS])
+# Use the system putenv even if it lacks GNU features, as we don't need them,
+# and the gnulib replacement runs afoul of a FreeBSD 10.1 bug; see Bug#19874.
+AC_CHECK_FUNCS_ONCE([putenv])
+AC_DEFUN([gl_FUNC_PUTENV],
+  [test "$ac_cv_func_putenv" = yes || REPLACE_PUTENV=1])
 
 # Initialize gnulib right after choosing the compiler.
 dnl Amongst other things, this sets AR and ARFLAGS.