qmake does not write all paths with native separators when generating Makefile

qmake does not write all paths with native separators when generating a Makefile.

For example, if a .pro file contains

link0.target=./a/b/c.bob
link0.depends=./a/y.jim
link0.commands=echo
QMAKE_EXTRA_TARGETS+=link0

the generated Makefile will contain the following rule on Windows:

./a/b/c.bob: a\y.jim
echo

All paths in the Makefile should be written with native separators.