ScopInfo: Add function to invalidate ScopArrayInfo object

In case the underlying basepointer of a ScopArrayInfo object is moved to another
module while the scop is still processed is it necessary to free dependent
ScopArrayInfo objects as they might otherwise be looked accidentally when a
new llvm basepointer value is reassigned the very same memory location as the
llvm value that has been moved earlier.

This function is not yet used in Polly itself, but is useful for external users.

llvm-svn: 262113