Vivado fixes

This fixes several problems I encountered when adding hdlmake building to gbaHD.

• There was a regression invoking vivado due to command formatting changes
• The project has known timing failures, and the check for success did not consider "completed with timing failures" a valid result. I'm not sure if this is a desirable change. Timing failures are not an impediment to generating a bitstream in the Vivado GUI, but it was causing make to exit with an error. Some users might prefer the strict behavior, though.
• All source files were being marked as "global includes". Vivado does not do this by default when adding sources to a project. It was causing strange import/name visibility errors during synthesis. If accessing this option is important, there needs to be a way to request it explicitly on certain files, such as a new manifest variable or the ability to add custom tcl to files.tcl.

I think the first bullet point is an unobjectionable bugfix, but the other two have some possible trade-offs. Let me know how you'd prefer to approach them.