v5.12.3

Mirror of 5.12.3 release sources

v5.9.1-p0: xcb depends on Xau

Fix check if xcb is static

v5.5.1-cvpixelbuffer-2-p9: iOS 10.0 fix

Cherry-pick of http://code.qt.io/cgit/qt/qtbase.git/commit/?h=dev&id=87b256c4359ddd4d29aec7db8962be81f80f79c3