VCS -top option is ambiguous

[harrisonliew]

According to the documentation, it is necessary for specifying the top-level configuration or module of the design (i.e. the testbench module). Unfortunately, TestDriver in Chipyard appears to be compiled by VCS, and thus specifying -top TestDriver leads to a module collision:

Error-[TMENF-ILL] Top Module/Entity not found
  Top module/entity/config "TestDriver" is not found in the following library
  list.
  Liblist: work


Error-[IRMINTM] Illegal module instantiations
  Illegal to have recursive module instantiations.
  No Top Modules Defined
  There should be at least one top module that is not instantiated by any
  other module.

ucb-bar/hammer-synopsys-plugins#34 made -top optional as a workaround for now.