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