[ARM] 3486/1: Mark memory as clobbered by the ARM _syscallX() macros

Patch from Markus Gutschke

In order to prevent gcc from making incorrect optimizations, all asm()
statements that define system calls should report memory as
clobbered. Recent versions of the headers for i386 have been changed
accordingly, but the ARM headers are still defective.

This patch fixes the bug tracked at
http://bugzilla.kernel.org/show_bug.cgi?id=6205



Signed-off-by: Markus Gutschke <markus@google.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>