* sverker/kernel/net_kernel-failed-accept_pending/ERL-781/OTP-15438:
  kernel: Fix bug in net_kernel for connection attempt from self

net_kernel crashed due to invalid return from handle_info.
Could only happen if erts_internal:new_connection fails
due to non-atom Node or if Node is the own node name.

* 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.