V4 JIT: save/restore ebx (GOT ptr) on linux/x86.

On linux/x86, ebx is used to store the global offset table. When using
this register for temporary values, we have to save it at the entry of
a generated function, and restore it before doing calls and at the end.

Task-number: QTBUG-36289
Change-Id: I30194be3ce44f58b793ee52f6201906bcb68d46a
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
V4: fix range sorting

When a life-time interval is split from another interval, it has to come
before an interval that starts at the same position but is not split.

This also means that a means that the all ranges in a split interval
are uses, which is important for allocation: all incoming parameters for
an operation need to be allocated before allocating a register for the
result as the result will only start its life "at the end" of the
operation.

This patch fixes a problem register allocation is done in a function
where register pressure is high (e.g. on platforms that have few
registers to start with). Specifically, crypto.js on x86 triggered it.

Change-Id: Iee3e5d82a887b8de573dfc23513844143d0c8073
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
V4 regalloc: fix interval splitting when register pressure is high.

When a register is needed for an interval, but none is available, one
of the used registers will be chosen and spilled to the stack (meaning
it will be split) before the current position. However, if a register
is used at the current position for an incoming parameter, its interval
has to be split after the current position. This patch adds/fixes the
latter case.

This fixes crypto.js on x86. The specific problem there was that the
result of an operation needed a register, and chose the one from one
of the incoming parameters (which then should get spilled/split).
However, this interval was already split, and started exactly at that
the current position. So splitting before the current position did
nothing, resulting in it staying alive and using the same register as
the result. So any subsequent use of would have the invalid value.

Task-number: QTBUG-36430
Change-Id: I228fc210b009aa0b16b08a374fc955fabfbb6d12
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>