6610 - tweak the Linux boot image generator

So far we hardcoded the translation process and it only supported SubX.
Now we pass in an ELF binary and outsource how it's generated.

tools/iso/linux

@@ -1,6 +1,6 @@
 #!/bin/sh
-# Build one or more .subx files into an ELF binary, and package it up into a
-# bootable ISO image with a Linux kernel.
+# Package up an ELF binary generated by Mu into a bootable ISO image with a
+# Linux kernel.
 #
 # Must be run on Linux, and from the top-level mu/ directory.
 #
@@ -11,20 +11,18 @@
 
 set -e
 
-if [ $# -eq 0 ]
+if [ $# -ne 1 ]
 then
-  echo "Usage: `basename $0` file.subx ..."
+  echo "Usage: `basename $0` <elf file>"
   exit 1
 fi
 
-echo "=== building SubX binary"
-./translate_subx $*
-mv a.elf init
-
 echo "=== constructing initramfs out of SubX binary"
 rm -rf tmp_linux/isoimage
 mkdir -p tmp_linux/isoimage/boot
+cp -i $1 init
 echo init | cpio -R root:root -H newc -o | xz -9 --check=none > tmp_linux/isoimage/boot/rootfs.xz
+rm init
 
 if [ ! -d kernel.linux ]
 then