bug#70026: QtBase 6.5.2: Wrong private header locations

[Daniel Ziltener via Bug reports for GNU Guix]

The private header files of QtBase (and probably other Qt packages as 
well) are placed in the wrong location. In my case, I am trying to use 
qmetaobjectbuilder_p.h. The path for it is 
/gnu/store/zywk3i6r200qd0w0fjizg3m5nwpkkzjs-profile/include/qt6/QtCore/6.5.2/QtCore/private/qmetaobjectbuilder_p.h 
(expected would be 
/gnu/store/zywk3i6r200qd0w0fjizg3m5nwpkkzjs-profile/include/qt6/QtCore/private/qmetaobjectbuilder_p.h), 
which leads to issues when compiling, because qmetaobjectbuilder_p.h 
contains an "#include <QtCore/private/qglobal_p.h>", which can then not 
be found. It also means I cannot use any of the provided include path 
env variables like C_INCLUDE_PATH.