boot2qt/embedded: Qt Creator fails to debug qtbase

Steps to reproduce:

• compile qtbase on a linux host
• cross compile it with the following configure options
  a) ../configure -developer-build -qt-host-path ~/Qt/6.6.0/gcc_64
  => Qt Creator will fail to deploy, run and debug e.g. the qtbase Menus example
  b) ../configure -debug -prefix /usr/local -qt-host-path ~/Qt/6.6.0/gcc_64
  => Qt Creator will fail to accept the build as a compile kit, because qmake is not compiled with it.
  c) ../configure -developer-build -prefix /usr/local -qt-host-path ~/Qt/6.6.0/gcc_64
  => Qt Creator will fail to deploy (Menu example), with the following error:

    Qt was configured as non-prefix build.  Installation is not supported for
    this arrangement.
  

  The FEATURE_no_prefix is set to OFF, however.
  (see: this bugreport)