Futurewei 20220120

Created by: noahsherrill

Summary of changes:

• Updated vector implementation to comply with V Extension Version 1.0
• Added support for Sv39
• Updated Spike version used by Handcar to 7dbb7c3
• Fixed the following issues:
  • Vector strided segment load/store instructions sometimes failed to generate due to miscalculation of the memory access boundary
  • The computed index register count was sometimes incorrect for vector indexed segment load/store instructions
  • Leaf megapage descriptors for data pages were sometimes encoded as non-leaf descriptors
  • Execution sometimes failed when the simulation attempted to speculatively read instructions past the end-of-test jump instruction
  • The build could fail if the defusedxml library was installed on the system
  • Miscellaneous other minor issues