QV4: Use QVarLengthArray in cleanupBasicBlocks.
QV4: Use QVarLengthArray in cleanupBasicBlocks.

Avoids heap allocations, drops around ~60ms off my morbid testcase in doing so.
QBitArray is still allocating, meaning this function isn't "free", but it's now
at 0.9% of runtime vs the 1.3% it was before, so something for another day.

Change-Id: Ie0db8e0312bde5f67b37250d04b4d65e1f0b034d
Reviewed-by: Simon Hausmann <a975102812d593b3191088e3d0aeaeb6f11dbcf5@digia.com>

matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative,matthewvogt/qtdeclarative