x86 throws away .discard section but no other archs do. Also,
.discard is not thrown away while linking modules. Make every arch
and module linking throw it away. This will be used to define dummy
variables for percpu declarations and definitions.

This patch is based on Ivan Kokshaysky's alpha percpu patch.

[ Impact: always throw away everything in .discard ]

Signed-off-by: Tejun Heo
Cc: Ivan Kokshaysky
Cc: Richard Henderson
Cc: Russell King
Cc: Haavard Skinnemoen
Cc: Bryan Wu
Cc: Mikael Starvik
Cc: Jesper Nilsson
Cc: David Howells
Cc: Yoshinori Sato
Cc: Tony Luck
Cc: Hirokazu Takata
Cc: Geert Uytterhoeven
Cc: Michal Simek
Cc: Ralf Baechle
Cc: Kyle McMartin
Cc: Benjamin Herrenschmidt
Cc: Paul Mackerras
Cc: Martin Schwidefsky
Cc: Heiko Carstens
Cc: Paul Mundt
Cc: David S. Miller
Cc: Jeff Dike
Cc: Chris Zankel
Cc: Rusty Russell
Cc: Ingo Molnar