Do not write Q_BYTE_ORDER to qconfig.h in the configures. Instead,
we #define Q_BYTE_ORDER in qprocessordetection.h, since many CPUs only
support a single endian format. For bi-endian processors, we set
Q_BYTE_ORDER depending on how the preprocessor sets __BYTE_ORDER__,
__BIG_ENDIAN__, or __LITTLE_ENDIAN__ (instead of using a compile test
to do so).

For operating systems that only support a single byte order, we can
check for Q_OS_* in addition to the preprocessor macros above. This is
possible because qprocessordetection.h is included by qglobal.h after
Q_OS_* and Q_CC_* detection has been done. Do this for Windows CE,
which is always little- endian according to MSDN.

Change-Id: I019a95e05252ef69895c4b38fbfa6ebfb6a943cd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>