Fix build failure on NetBSD/arm.

patch-ad:
src/tools/qglobal.h mentionss about Q_NO_PACKED_REFERENCE:
---
/* ARM gcc pads structs to 32 bits, even when they contain a single
  char, or short.  We tell gcc to pack QChars to 16 bits, to avoid
  QString bloat. However, gcc 3.4 doesn't allow us to create references to
  members of a packed struct. (Pointers are OK, because then you
  supposedly know what you are doing.) */
#  if (defined(__arm__) || defined(__ARMEL__)) && !defined(QT_MOC_CPP)
#    define Q_PACKED __attribute__ ((packed))
#    if __GNUC__ == 3 && __GNUC_MINOR__ >= 4
#      define Q_NO_PACKED_REFERENCE
---
but it seems we also have to define it on gcc4.

patch-ch:
Furthermore, it looks gcc4 also rejects implicit pointer casts, so
add an explicit cast where the above Q_NO_PACKED_REFERENCE is referred.

(tsutsui)