V4 JIT: fix MSVC warning.

d:\dev\qt5-dev\qtdeclarative\src\qml\jit\qv4assembler_p.h(394) : warning C4146: unary minus operator applied to unsigned type, result still unsigned

Change-Id: Iff972f419d7505ecedeb42b4b7eb456295225cb2
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
V4 JIT: enable disassembler on windows.

Change-Id: I55a2a96a1a774c79cc2146c6b47d441fede1d102
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>