The file exists in C:\dev\qt5-dev-d\qtvirtualkeyboard\src\virtualkeyboard\.rcc\debug, not C:\dev\qt5-dev-d\qtvirtualkeyboard\src\virtualkeyboard\.rcc.
andysh found out that the problem is this line; commenting that out and then re-running qmake works.
The output of qmake -d -d is attached:
debug.7z