V4: changed environment variable SHOW_CODE.

Use QV4_SHOW_ASM for the generated assembly from the JIT, and use
QV4_SHOW_IR to get dumps of the IR.

Change-Id: Id85d3d6c87b47088c312475a7c737d54c58c7791
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
V4: remove inplace operations

Inplace operations are expanded when building the IR, so the neither the
IR, nor the instruction selection backends or runtime need to handle
them.

Change-Id: Id01f9544e137dd52364cf2ed2c10931c31ddfff3
Reviewed-by: Lars Knoll <lars.knoll@digia.com>