qmake -project produces unescaped backslashes to be used in the DEPENDPATH on Windows where there are multi-level subdirectories

qmake project generator causes \ to be used in the DEPENDPATH items where -recursive is used and where there is more than one level of subdirectories. This isn't a problem but causes the "unescaped backslashes are deprecated" warning when running qmake on the resultant .pro file. This could cause problems if/when unescaped backslashes are no longer supported.

The problem can be reproduced using a directory structure like this:-

C:\Temp\qtbug\inc
C:\Temp\qtbug\src
C:\Temp\qtbug\inc\file.h
C:\Temp\qtbug\src\a
C:\Temp\qtbug\src\b
C:\Temp\qtbug\src\file.cpp
C:\Temp\qtbug\src\a\file_a.cpp
C:\Temp\qtbug\src\b\file_b.cpp

and a qmake line like this:-

qmake -project -o qtbug.pro -r src inc

from the qtbug directory.