treewide: Use <ulink> instead of <filename> for man pages

"gcc(1)" is really not a file name.

Use <ulink> and link to the online man page on
https://man.archlinux.org/ so the user can refer to the man pages more
easily.

The change is done via a sed command and long lines are wrapped
manually.

chapter10/fstab.xml

@@ -56,7 +56,7 @@ EOF</userinput></screen>
   class="partition">sda2</filename>, <filename
   class="partition">sda5</filename>, and <systemitem
   class="filesystem">ext4</systemitem>. For details on the six
-  fields in this file, see <filename>fstab(5)</filename>.</para>
+  fields in this file, see <ulink role='man' url='&man;fstab.5'>fstab(5)</ulink>.</para>
 
   <para>Filesystems with MS-DOS or Windows origin (i.e. vfat, ntfs, smbfs,
   cifs, iso9660, udf) need a special option, utf8, in order for non-ASCII

chapter10/kernel.xml

@@ -324,7 +324,8 @@
     located in <xref linkend="ch-config-udev"/> and in the kernel
     documentation in the <filename
     class="directory">linux-&linux-version;/Documentation</filename> directory.
-    Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
+    Also, <ulink role='man' url='&man;modprobe.d.5'>modprobe.d(5)</ulink>
+    may be of interest.</para>
 
     <para>Unless module support has been disabled in the kernel configuration,
     install the modules with:</para>