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>

1 files changed, 35 insertions, 0 deletions

diff --git a/nss/grp-merge.h b/nss/grp-merge.h
new file mode 100644
index 0000000000..9e1f75cfc7
--- /dev/null
+++ b/nss/grp-merge.h
@@ -0,0 +1,35 @@
+/* Group merging implementation.
+   Copyright (C) 2016-2023 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/>.  */
+
+#ifndef _GRP_MERGE_H
+#define _GRP_MERGE_H 1
+
+#include <grp.h>
+
+/* Duplicate a grp struct (and its members). When no longer needed, the
+   calling function must free(newbuf).  */
+int
+__copy_grp (const struct group srcgrp, const size_t buflen,
+	    struct group *destgrp, char *destbuf, char **endptr);
+
+/* Merge the member lists of two grp structs together.  */
+int
+__merge_grp (struct group *savedgrp, char *savedbuf, char *savedend,
+	     size_t buflen, struct group *mergegrp, char *mergebuf);
+
+#endif /* _GRP_MERGE_H */