files in a 'files.XXX' file, config allows non-FreeBSD source files
with the same name as a FreeBSD source file to override the latter,
and in this situation it issues a warning.
However, if one of the user-specified files is actually a FreeBSD
source file (perhaps your kernel has some custom option that requires
that file), config mistakenly thinks it's a completely new file
and goes ahead and overrides all previous information for that file
(and issues the warning).
Fix this.
With help from: julian
1e306bb1c6