[RFC 5/6] msqid: Provide internal copy of struct __msqid64_ds

[Lukasz Majewski <lukma@denx.de>]

After the commit SHA1: 3283f711132eaadc4f04bd8c1d84c910c29ba
"sysv: linux: Add 64-bit time_t variant for msgctl"

The glibc internal, 64 bit supporting version of struct __msqid64_ds has
been exported.

This approach has issue when one would like to add Y2038 support to glibc.
The problem is that both struct msqid_ds and __msqid64_ds rely on exported
implementation of the msg.h header (./sysvipc/sys/msg.h) which
unconditionally includes ./sysdeps/unix/sysv/linux/bits/msq.h which in
turn includes ./sysdeps/unix/sysv/linux/bits/types/struct_msqid_ds.h

As a result the externally exported struct msqid_ds.h is used internally
by glibc. Problem starts when one wants to extend this struct with 64 bit
time support:

| In file included from ../sysdeps/unix/sysv/linux/bits/msq.h:28,
|                  from ../sysvipc/sys/msg.h:30,
|                  from ../sysdeps/unix/sysv/linux/include/sys/msg.h:2,
|                  from ../include/sys/msg.h:1,
|                  from ../sysdeps/unix/sysv/linux/msgctl.c:19:
| ../sysdeps/unix/sysv/linux/bits/types/struct_msqid_ds.h:31:6: error:
            "__USE_TIME_BITS64" is not defined, evaluates to 0 [-Werror=undef]
|  # if __USE_TIME_BITS64
|       ^~~~~~~~~~~~~~~~~


To fix this issue - the internal,for glibc, copy of struct __msqid64_ds
has been re-introduced. This will allow clear separation between exported
and internal glibc types.

Moreover, the __TIMESIZE based alias shall be internal to glibc.

Build tests:
./src/scripts/build-many-glibcs.py glibcs
---
 include/bits/types/struct_msqid64_ds.h        | 36 +++++++++++++++++++
 .../sysv/linux/bits/types/struct_msqid64_ds.h |  4 ---
 2 files changed, 36 insertions(+), 4 deletions(-)
 create mode 100644 include/bits/types/struct_msqid64_ds.h

diff --git a/include/bits/types/struct_msqid64_ds.h b/include/bits/types/struct_msqid64_ds.h
new file mode 100644
index 0000000000..8c39a2a872
--- /dev/null
+++ b/include/bits/types/struct_msqid64_ds.h
@@ -0,0 +1,36 @@
+/* Internal for glibc implementation of the SysV message struct msqid64_ds.
+   Copyright (C) 2020 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 <time.h>
+
+#if __TIMESIZE == 64
+# define __msqid64_ds msqid_ds
+#else
+struct __msqid64_ds
+{
+  struct ipc_perm msg_perm;	/* structure describing operation permission */
+  __time64_t msg_stime;		/* time of last msgsnd command */
+  __time64_t msg_rtime;		/* time of last msgsnd command */
+  __time64_t msg_ctime;		/* time of last change */
+  __syscall_ulong_t __msg_cbytes; /* current number of bytes on queue */
+  msgqnum_t msg_qnum;		/* number of messages currently on queue */
+  msglen_t msg_qbytes;		/* max number of bytes allowed on queue */
+  __pid_t msg_lspid;		/* pid of last msgsnd() */
+  __pid_t msg_lrpid;		/* pid of last msgrcv() */
+};
+#endif
diff --git a/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
index 3536c8ea62..07cc1036ab 100644
--- a/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
+++ b/sysdeps/unix/sysv/linux/bits/types/struct_msqid64_ds.h
@@ -20,9 +20,6 @@
 # error "Never use <bits/msq.h> directly; include <sys/msg.h> instead."
 #endif
 
-#if __TIMESIZE == 64
-# define __msqid64_ds msqid_ds
-#else
 struct __msqid64_ds
 {
   struct ipc_perm msg_perm;	/* structure describing operation permission */
@@ -35,4 +32,3 @@ struct __msqid64_ds
   __pid_t msg_lspid;		/* pid of last msgsnd() */
   __pid_t msg_lrpid;		/* pid of last msgrcv() */
 };
-#endif
-- 
2.20.1