build-aux: Refresh list of nonreentrant functions

There's a new twalk() function that has a reentrant variant. Add
the former onto list of nonreentrant functions.

Also, refresh the comment on how to get the list, because it's
outdated a bit.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

build-aux/Makefile.nonreentrant

@@ -15,17 +15,17 @@
 ## <http://www.gnu.org/licenses/>.
 
 #
-# Generated by running the following on Fedora 26:
+# Generated by running the following on current Gentoo:
 #
-#  nm -D --defined-only /lib64/libc.so.6 \
+#  nm -D --defined-only --without-symbol-versions /lib64/libc.so.6 \
 #      | grep '_r$' \
 #      | awk '{print $3}' \
-#      | grep -v __ \
-#      | grep -v qsort \ # Red herring since we don't need to pass extra args to qsort comparator
-#      | grep -v readdir \ # This is safe as long as each DIR * instance is only used by one thread
-#      | sort \
-#      | uniq \
-#      | sed -e 's/_r//'
+#      | grep -v -e '^_' -e 'qsort' -e 'readdir' \
+#      | sort -u \
+#      | sed -s 's/_r$//'
+#
+# qsort() is safe because we don't need to pass extra args to qsort comparator,
+# readdir*() is safe as long as each DIR * instance is only used by one thread.
 #
 # Also manually add in all inet_* functions some of which
 # are not threadsafe and do not have _r variants. They are
@@ -94,8 +94,8 @@ NON_REENTRANT += nrand48
 NON_REENTRANT += ptsname
 NON_REENTRANT += qecvt
 NON_REENTRANT += qfcvt
-NON_REENTRANT += random
 NON_REENTRANT += rand
+NON_REENTRANT += random
 NON_REENTRANT += seed48
 NON_REENTRANT += setstate
 NON_REENTRANT += sgetsgent
@@ -106,6 +106,7 @@ NON_REENTRANT += strerror
 NON_REENTRANT += strtok
 NON_REENTRANT += tmpnam
 NON_REENTRANT += ttyname
+NON_REENTRANT += twalk
 NON_REENTRANT += inet_addr
 NON_REENTRANT += inet_aton
 NON_REENTRANT += inet_lnaof