ARM: Fix register misuse bug in Allocate().

ARM: Fix register misuse bug in Allocate().

The bug is triggered if flags contains DOUBLE_ALIGNMENT and the
object_size is not an ARM immediate value. In this case, the code
for DOUBLE_ALIGNMENT uses the scratch2 register, which is aliased
to obj_size_reg containing the object_size.

Instead of pre-loading the object_size, which is difficult since
we are out of registers here, we simply generate a non-empty
sequence of add instructions for the addition of the constant
object_size (carefully handling possible overflow in each step).

Also turn static ASSERT into STATIC_ASSERT in Allocate().

BUG=v8:2851
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16221

[Benedikt Meurer, 2013-08-19 11:21:53]

PTAL

[Sven Panne, 2013-08-19 12:50:27]

lgtm

[Benedikt Meurer, 2013-08-19 13:38:05]

Committed patchset #1 manually as r16221.