Merge branch 'nd/warn-more-for-devs'

Merge branch 'nd/warn-more-for-devs'

The build procedure "make DEVELOPER=YesPlease" learned to enable a
bit more warning options depending on the compiler used to help
developers more.  There also is "make DEVOPTS=tokens" knob
available now, for those who want to help fixing warnings we
usually ignore, for example.

* nd/warn-more-for-devs:
  Makefile: add a DEVOPTS to get all of -Wextra
  Makefile: add a DEVOPTS to suppress -Werror under DEVELOPER
  Makefile: detect compiler and enable more warnings in DEVELOPER=1
  connect.c: mark die_initial_contact() NORETURN