[OpenSmalltalk/opensmalltalk-vm] ce7f66: Fix issue #557 (workaround?)

 
  Branch: refs/heads/issue_557_export_conflict_on_windows
  Home:   https://github.com/OpenSmalltalk/opensmalltalk-vm
  Commit: ce7f664825a5640bdf45a94f83357827f25353e6
      https://github.com/OpenSmalltalk/opensmalltalk-vm/commit/ce7f664825a5640bdf45a94f83357827f25353e6
  Author: Nicolas Cellier <[hidden email]>
  Date:   2021-04-20 (Tue, 20 Apr 2021)

  Changed paths:
    M platforms/Cross/vm/sqAssert.h

  Log Message:
  -----------
  Fix issue #557 (workaround?)

If we build an internal plugin `SQUEAK_BUILTIN_PLUGIN`, then we don't need to `EXPORT` the error/warning functions.
There are still conflicting definitions in sqVirtualMachine.h which totally ignore IMPORT/EXPORT but these only generate warnings, not errors.