Vivado fixes

Rebased on develop.

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

• The project has known timing failures, and the check for success did not consider "completed with timing failures" a valid result. I added an option to allow proceeding with timing failures.
• 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, adding custom tcl should allow it.