AIX: Fix DoubleToInteger.

AIX std::ceil() does not return negative zero.
PPC: reduce code size with stubs for reg save/restore.
PPC: remove unused WriteInt32ToHeapNumberStub.
Fix alignment of Code::kConstantPoolOffset.
PPC: prefer li vs. constant pool load when no relocation.
PPC: perf enhancement: clean up store-with-update usage.
PPC: perf enhancement: improve CopyCharsUnsigned non-conversion cases.
PPC: perf enhancement: improve prologue performance.

Pass code entry address in ip for use by constant pool pointer
initialization and code aging logic.
PPC: perf enhancement: use bctrl for calls (vs blrl).
PPC: perf enhancement: optimize LeaveFrame.
PPC: perf enhancement: optimize Allocate.
PPC: perf enhancement: optimize AddAndCheckForOverflow when rhs is an immediate value.

Conflicts:

	src/ppc/lithium-codegen-ppc.cc
Work around gcc compiler bug.
PPC: perf enhancement: detect recursive calls.
PPC: perf enhancement: tune kPageSizeBits and kCodeSizeMultiplier.

Conflicts:

	src/heap/heap.cc
	test/cctest/test-spaces.cc
PPC: perf enhancement: remove sign extension for non-overflow integer add/sub.

Conflicts:

	src/ppc/lithium-codegen-ppc.cc

Conflicts:

	src/ppc/lithium-codegen-ppc.cc
PPC: perf enhancement: prefer isel over branch logic.

Conflicts:

	src/globals.h
	src/ppc/lithium-codegen-ppc.cc
PPC: fix simulation of isel instruction.
PPC: perf enhancement: additional isel opportunities.

Conflicts:

	src/ppc/code-stubs-ppc.cc
PPC: perf enhancement: optimize sign extension logic.

Conflicts:

	src/ppc/lithium-codegen-ppc.cc