Don't use deprecated functions on Mac OS X

Don't use deprecated functions on Mac OS X

io/qfilesystemwatcher_fsevents.cpp:346:15: warning: 'stat64' is
deprecated [-Wdeprecated-declarations]
        if (::stat64(it->absolutePath, &newInfo) == 0) {
              ^

According to 'man 2 stat' on Mac OS X, the stat64() function is
deprecated in 10.6 and above. Instead, we are supposed to define
the _DARWIN_USE_64_BIT_INODE which enables the 64-bit ino_t member in
the stat struct and uses function symbol suffixes to call the correct
version of stat with 64-bit inode support.

Change-Id: I697374186c7f4d69df783f06962ca5644222194d
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>