Dont update makewhatis files if they're on readonly filesystems

http://bugs.gentoo.org/163932

--- src/makewhatis.sh
+++ src/makewhatis.sh
@@ -184,6 +188,25 @@
      if [ x$verbose != x ]; then
 	echo "about to enter $mandir" > /dev/stderr
      fi
+
+     # kludge for Slackware's /usr/man/preformat
+     if [ $mandir = /usr/man/preformat ]
+     then
+	mandir1=/usr/man
+     else
+	mandir1=$mandir
+     fi
+
+     # if $mandir is on a readonly partition and we cannot update the whatis
+     # file, then let's simply skip it
+     if ! touch ${mandir1}/whatis 2> /dev/null
+     then
+	if [ x$verbose != x ]; then
+	   echo skipping $mandir - whatis file is readonly > /dev/stderr
+	fi
+	continue
+     fi
+
      if [ -s ${mandir}/whatis -a $pages = man -a x$update = x ]; then
 	if [ x$verbose != x ]; then
 	   echo skipping $mandir - we did it already > /dev/stderr
@@ -407,14 +430,6 @@
 
        cd $here
 
-       # kludge for Slackware's /usr/man/preformat
-       if [ $mandir = /usr/man/preformat ]
-       then
-	 mandir1=/usr/man
-       else
-	 mandir1=$mandir
-       fi
-
        if [ -f ${mandir1}/whatis ]
        then
 	 cat ${mandir1}/whatis >> $TMPFILE