Makefile: Fix double escaping when DEPFILE is used

In commit cfd8a5ac1f (Makefiles: Add support of DEPFILE for
add_custom_command, 2020-12-04, v3.20.0-rc1~237^2~1) we added a
`ConvertToOutputPath` call on a path given to the `depends` field of
`WriteMakeRule`.  The latter already handles escaping for Makefile
syntax.

Fixes: #25554
4 files changed