Silence MinGW/gcc-4.8.1 compiler warnings.

Reorder V4::Object's and V4::Value's private object inline functions
such that its definitions are visible from where they are being
referenced.

qv4object_p.h:418:13: warning: 'uint QV4::Object::arrayLength() const'
redeclared without dllimport attribute after being referenced with dll
linkage

qv4object_p.h:430:13: warning:
'void QV4::Object::setArrayLengthUnchecked(uint)' redeclared without
dllimport attribute after being referenced with dll linkage

Change-Id: I49a3c9d1da637eaf038f53b29ec13c35253de9f1
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>