* spawn.cc (child_info_spawn::worker): Eliminate call to newargv.set() in favor

* spawn.cc (child_info_spawn::worker): Eliminate call to newargv.set() in favor
of conglomerated newargv.setup().  Let newargv.setup() decide when to call
dup_all().  Only set argc and argv for cygwin processes.
(av::setup): Rename from av::fixup.  Accept argc and argv parameters.  Fill out
argv and argc here.  Duplicate whole argv structure when this is a Cygwin
executable.
* winf.cc (linebuf::fromargv): Don't bother duplicating argv elements since
they will never be used.
* winf.h (av::set): Delete.
(av::setup): Rename from av::fixup.  Add two parameters.
(av::replace0_maybe): Assign calloced to 1 rather than 'true' for clarity.
(av::dup_maybe): Delete.
(av::dup_all): Set calloced to show that we have duplicated all of the
arguments in the list.