Previously the data from before the exec was kept in there. Zero
them instead.

[ tglx: arch/x86 adaptation ]
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>