Note: Some of the fixes are for newlib in general but not NaCl-specific.

* include/ruby/intern.h (rb_fd_select): declare struct timeval, or the
  struct gets local to the function in C99.

* file.c (#include): add nacl/stat.h for PNaCl.
  (utimes): added a declaration for PNaCl.
  (stat_atimespec): stat::st_atimensec is long long but
  timespec::tv_nsec is long in PNaCl.
  (stat_mtimespec, stat_ctimespec): ditto.
  (rb_group_member): disable getgroups unless HAVE_GETGROUPS.
  (eaccess): unify the fallback to generic defined(USE_GETEUID).

* io.c: include sys/time.h for struct timeval.
  (rb_close_before_exec): nothing we can do if F_GETFD is not
  available.
  (ioctl): pnacl newlib actually doesn't have ioctl.

* process.c (maxgroups): it is used iff
   defined(_SC_NGROUPS_MAX) || defined(NGROUPS_MAX) but not
   defined(HAVE_GETGROUPS) || defined(HAVE_SETGROUPS).
  (obj2gid): fail unless the object is a Fixnum if getgrnam is not
  available.
  (disable_child_handler_fork_child): sigaction is not available in
  PNaCl newlib.

* configure.in (warnflags, strict_warnflags): avoid -ansi for strlcpy.
  (rb_cv_gcc_atomic_builtins): also check
  __atomic_or_etch because it is used in ruby_atomic.h.
  (rb_cv_gcc_sync_builtins): ditto.
  (HAVE_GETGRNAM): added.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47882 b2dd03c8-39d4-4d8f-98ff-823fe69b080e