Add international character support for makefile dependency filenames

While C does not allow non-ASCII characters in #include filenames, D does allow international characters in imported modules. D module dependencies work similarly to C #include dependencies. Other languages may be using the depfile feature of ninja in a similar way, so forbidding international characters in makefile dependency filenames is a needless limitation.

This patch treats characters greater than 127 as text, rather than as whitespace, in depfiles. A test is also added to verify that these characters are handled correctly.