Revert the mode_t -> int changes and add a warning in the BUGS section instead.

While FreeBSD's implementation of these expect an int inside of libc, that's an
implementation detail that we can hide from the user as it's the natural
promotion of the current mode_t type and before it is used in the kernel, it's
converted back to the narrower type that's the current definition of mode_t. As
such, documenting int is at best confusing and at worst misleading. Instead add
a note that these args are variadic and as such calling conventions may differ
from non-variadic arguments.

lib/libc/sys/mq_open.2

@@ -37,7 +37,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 15, 2014
+.Dd September 28, 2019
 .Dt MQ_OPEN 2
 .Os
 .Sh NAME
@@ -133,7 +133,7 @@ Create a message queue.
 It requires two additional arguments:
 .Fa mode ,
 which is of type
-.Vt int ,
+.Vt mode_t ,
 and
 .Fa attr ,
 which is a pointer to an
@@ -317,6 +317,13 @@ This implementation places strict requirements on the value of
 it must begin with a slash
 .Pq Ql /
 and contain no other slash characters.
+.Pp
+The
+.Fa mode
+and
+.Fa attr
+arguments are variadic and may result in different calling conventions
+than might otherwise be expected.
 .Sh COPYRIGHT
 Portions of this text are reprinted and reproduced in electronic form
 from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --

lib/libc/sys/open.2

@@ -28,7 +28,7 @@
 .\"     @(#)open.2	8.2 (Berkeley) 11/16/93
 .\" $FreeBSD$
 .\"
-.Dd September 17, 2019
+.Dd September 28, 2019
 .Dt OPEN 2
 .Os
 .Sh NAME
@@ -61,7 +61,7 @@ In this case
 and
 .Fn openat
 require an additional argument
-.Fa "int mode" ,
+.Fa "mode_t mode" ,
 and the file is created with mode
 .Fa mode
 as described in
@@ -615,3 +615,8 @@ permits searches.
 The present implementation of the
 .Fa openat
 checks the current permissions of directory instead.
+.Pp
+The
+.Fa mode
+argument is variadic and may result in different calling conventions
+than might otherwise be expected.