Have (so far) bumped into two apparent errors in header files for Qt 5.11.0.  The two files are:

.../5.11.0/src/qtbase/include/QtEventDispatcherSupport/5.11.0/QtEventDispatcherSupport/private/qwindowsguieventdispatcher_p.h

.../5.11.0/src/qtbase/include/QtWindowsUIAutomationSupport/5.11.0/QtWindowsUIAutomationSupport/private/qwindowsuiawrapper_p.h

In each case, these header files include one line of the form:

#include "../../../../../src/platformsupport/.....

There are one too many "../" in each - 5 instead of 4.  With that modification, compilation completes correctly.  I suspect there will be additional such errors and will compile a list.

However, since this appears to be a configuration anomaly, I thought it worth reporting early.