configure: Write new file "config-all-disas.mak" when running configure

Incremental builds added new lines to that file each time when configure
was run.

Now a new file with a comment line is written.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/configure b/configure
index cc1e20a..9538041 100755
--- a/configure
+++ b/configure
@@ -3314,6 +3314,8 @@
 config_host_mak="config-host.mak"
 config_host_ld="config-host.ld"
 
+echo "# Automatically generated by configure - do not modify" >config-all-disas.mak
+
 echo "# Automatically generated by configure - do not modify" > $config_host_mak
 printf "# Configured with:" >> $config_host_mak
 printf " '%s'" "$0" "$@" >> $config_host_mak