~ generalize verilator variables:
  QUIT_ON_VERILATOR_ERRORS -> QUIT_ON_LINTER_ERRORS
  QUIT_ON_VERILATOR_WARNINGS -> QUIT_ON_LINTER_WARNINGS
  VERILATOR_RELATIVE_INCLUDES -> LINTER_RELATIVE_INCLUDES
  RUN_VERILATOR -> RUN_LINTER
+ add LINTER_INCLUDE_PDK_MODELS
+ add LINTER_DEFINES
+ include verilator in ci tool updater
- do not include pdk verilog models using -I
- remove workaround for verilator std error
- disallow timing constructs. Print an error to the user to remove or guard them.