Fix minor bugs in Vivado TCL generation

[sgherbst]

This PR fixes two small issues in the way TCL files are generated for running Vivado simulations.

• `define macros containing literal double-quotes are now supported. This already seems to be supported in the other simulators.
• Paths with spaces are now supported (for the build directory, source files, library files, and include directories). The only other simulator that seems to support this is iverilog.

Though minor, these updates are useful for me because they allow me to pass path information into Verilog code via `define macros (e.g., the path to a file to be used for $readmemb).

[leonardt]

LGTM