headers_install.pl: convert to headers_install.sh

Remove perl from make headers_install by replacing a perl script (doing a
simple regex search and replace) with a smaller, faster, simpler,
POSIX-2008 shell script implementation.  The new shell script is a single
for loop calling sed and piping its output through unifdef to produce the
target file.

Same as last time except for minor tweak to deal with code review from
here: http://lkml.indiana.edu/hypermail/linux/kernel/1302.3/00078.html

(Note that this drops the "arch" argument, which isn't used. Kbuild
already points to the right input files on the command line.)

Signed-off-by: Rob Landley <rob@landley.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowell@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>