Remove 'grp' and merge into 'nss' and 'posix'

The majority of grp routines are entry points for nss functionality.
This commit removes the 'grp' subdirectory and moves all nss-relevant
functionality and all tests to 'nss', and the 'setgroups' stub into
'posix' (alongside the 'getgroups' stub).  References to grp/ are
accordingly changed.  In addition, compat-initgroups.c, a fallback
implementation of initgroups is renamed to initgroups-fallback.c so that
the build system does not confuse it for nss_compat/compat-initgroups.c.

Build time improves very slightly; e.g. down from an average of 45.5s to
44.5s on an 8-thread mobile x86_64 CPU.
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

3 files changed, 33 insertions, 1 deletions

diff --git a/posix/Makefile b/posix/Makefile
index c36b9d9..be7d319 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -137,6 +137,7 @@ routines := \
   sched_sets \
   sched_yield \
   setgid \
+  setgroups \
   setpgid \
   setpgrp \
   setresgid \
diff --git a/posix/Versions b/posix/Versions
index 3753810..2eedbc3 100644
--- a/posix/Versions
+++ b/posix/Versions
@@ -53,7 +53,7 @@ libc {
     sched_get_priority_max; sched_get_priority_min; sched_getparam;
     sched_getscheduler; sched_rr_get_interval; sched_setparam;
     sched_setscheduler; sched_yield; setegid; seteuid; setgid;
-    setpgid; setpgrp; setsid; setuid; sleep; sysconf;
+    setgroups; setpgid; setpgrp; setsid; setuid; sleep; sysconf;
 
     # t*
     times;
diff --git a/posix/setgroups.c b/posix/setgroups.c
new file mode 100644
index 0000000..d988866
--- /dev/null
+++ b/posix/setgroups.c
@@ -0,0 +1,31 @@
+/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <sys/types.h>
+#include <grp.h>
+
+/* Set the group set for the current user to GROUPS (N of them).  */
+int
+setgroups (size_t n, const gid_t *groups)
+{
+  __set_errno (ENOSYS);
+  return -1;
+}
+libc_hidden_def (setgroups)
+
+stub_warning (setgroups)