Previously if the jobserver was active, MAKEFLAGS would contain only
the -j option but not the number (not -j5 or whatever) so users
could not discover that value. Allow that value to be provided in
MAKEFLAGS without error but still give warnings if -jN is provided
on the command line if the jobserver is already activated.
* NEWS: Discuss the new behavior.
* os.h, posixos.c, w32/w32os.c: Return success/failure from
jobserver_setup() and jobserver_parse_auth().
* main.c (main): Separate the command line storage of job slots (now
in arg_job_slots) from the control storage (in job_slots). Make a
distinction between -jN flags read from MAKEFLAGS and those seen
on the command line: for the latter if the jobserver is enabled then
warn and disable it, as before.
* tests/scripts/features/jobserver: Add new testing.
* NEWS: Mention the change.
* main.c: Rename jobserver_fds variable to jobserver_auth and
--jobserver-fds option to --jobserver-auth.
* os.h, posixos.c, w32/w32os.c: Rename jobserver_parse_arg() and
jobserver_get_arg() to jobserver_parse_auth()/jobserver_get_auth().
Testing has shown that vfork() is actually significantly
more efficient on systems where it's supported, even for
copy-on-write implementations. If make is big enough,
duplicating the page tables is significant overhead.
* configure.ac: Check for fork/vfork.
* makeint.h: Include vfork.h and set up #define for it.
* os.h, posixos.c (get_bad_stdin): For children who can't use
the normal stdin file descriptor, get a broken one.
* job.c (start_job_command): Avoid so many ifdefs and simplify
the invocation of child_execute_job()
(child_execute_job): move the fork operation here so it can
return early for the parent process. Switch to use vfork().
* function.c (func_shell_base): Use new child_execute_job() and
simplify ifdefs.
* job.h, main.c, remote-cstms.c, vmsjobs.c, w32os.c: Update
declarations and calls.
