Merge remote-tracking branch 'origin/5.5' into 5.6

Conflicts:
	config.tests/common/atomic64/atomic64.cpp
	configure
	src/3rdparty/forkfd/forkfd.c
	src/corelib/io/forkfd_qt.cpp
	src/widgets/kernel/qwidgetwindow.cpp
	tests/auto/corelib/statemachine/qstatemachine/tst_qstatemachine.cpp
	tests/auto/network/socket/qtcpsocket/tst_qtcpsocket.cpp
	tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp
	tools/configure/configureapp.cpp

Change-Id: Ic6168d82e51a0ef1862c3a63bee6722e8f138414