Release 5.0.0-pre.20210708.4 (2021-07-16)

Baseline: ca1d20fd

Cherry picks:

   + 802901e6:
     Add flags parameter to attr.label for use in builtins only.
   + aa768ada:
     Automated rollback of commit
     ca1d20fd.
   + 4bcf2e83:
     Automated rollback of commit
     ff38dbfc.
   + 706483fd:
     Resolve merge conflict
   + 3821db87:
     Fix merge conflict properly

Important changes:

  - The used_heap_size_post_build field in BEP is populated when the
    --memory_profile flag is set

This release contains contributions from many people at Google, as well as Daniel Wagner-Hall, Grzegorz Lukasik, Keith Smiley, Kevin Hogeland, Yannic Bonenberger.