* john/erts/spectre-configure-flag-otp_20/OTP-15430/ERIERL-237:
  Allow disabling retpoline in interpreter loop
  Add a ./configure flag for spectre mitigation

* john/erts/spectre-configure-flag/OTP-15430/ERIERL-237:
  Allow disabling retpoline in interpreter loop
  Add a ./configure flag for spectre mitigation

We only do this when the user has explicitly told us it's okay to
partially disable mitigation (spectre-mitigation=incomplete). The
macro is inert if it isn't.

Note that the ERTS_NO_RETPOLINE macro introduced by this commit is
completely inert unless spectre-mitigation is set to 'incomplete.'
This includes when mitigation has been manually enabled through
CFLAGS, so it should be impossible for it to unintentionally
disable mitigation.

* john/erts/defer-orphan-file-close/OTP-15421/ERIERL-261:
  Fix broken assertion on monitor release
  Avoid closing files in gc/monitor callbacks

* ingela/public_key/DSA-SHA2/OTP-15367:
  public_key: Add additional ASN-1 definitions for DSA SHA2 support
  public_key: Add DSA with SHA2 support