MIPS: Fix and simplify code aging.

MIPS: Fix and simplify code aging.

This commit fixes a lot of test failures that we saw earlier in the buildbots (http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20mips%20-%20sim/builds/3034/steps/Check/logs/stdio).

In some very rare cases the code age stub address can be 0xXXXX0000 and in this case the li maco instruction emits only 1 instruction (instead of the expected 2). Thus the code age sequence will be 6 instructions long instead of 7, which breaks the code aging feature. This change makes sure that li always emits 2 instructions and it also simplifies the code aging sequence.

Also fixes a small mistake in the simulator at the jalr instruction.

BUG=
R=gergely@homejinni.com

Committed: https://code.google.com/p/v8/source/detail?r=18030

[palfia, 2013-11-22 16:15:26]

PTAL.

[dusmil, 2013-11-22 17:17:48]

Looks Good To Me.

[kisg, 2013-11-22 17:52:26]

LGTM

[palfia, 2013-11-22 18:14:06]

Committed patchset #1 manually as r18030 (presubmit successful).