unifdef: update to upstream version 2.5

Fix a long-standing cpp compatibility bug. The -DFOO argument
(without an explicit value) should define FOO to 1 not to the empty
string.

Add a -o option to support overwriting a file in place, and a -S
option to list the nesting depth of symbols. Include line numbers
in debugging output. Support CRLF newlines.

Signed-off-by: Tony Finch <dot@dotat.at>
Signed-off-by: Michal Marek <mmarek@suse.cz>