V4 JIT: fix stack use below stack pointer

V4 JIT: fix stack use below stack pointer

When storing a double value returned from a function call on platforms
where the value wouldn't fit in a register, we used to store it on the
stack and then load it into a FP register. This stack use was done
without first lowering the stack pointer.

For x86 and ARM, the value is loaded directly into the FP register, and
for other non-64-bit platforms it correctly allocates the stack slot.

Change-Id: Idbc260038958a036ac2a7383d845199626decc8e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>