Replace the vague, incorrect, and confusing BUGS sections with CAVEATS

clearly stating which arguments have to be avoided, and mention the
header files defining the constants required for the checks.
Feedback and OK guenther@, OK bluhm@.

src/lib/libc/stdlib/abs.3

@@ -29,15 +29,16 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: abs.3,v 1.11 2013/07/17 05:42:11 schwarze Exp $
+.\"	$OpenBSD: abs.3,v 1.12 2019/01/18 07:32:17 schwarze Exp $
 .\"
-.Dd $Mdocdate: July 17 2013 $
+.Dd $Mdocdate: January 18 2019 $
 .Dt ABS 3
 .Os
 .Sh NAME
 .Nm abs
 .Nd integer absolute value function
 .Sh SYNOPSIS
+.In limits.h
 .In stdlib.h
 .Ft int
 .Fn abs "int j"
@@ -66,5 +67,9 @@ The
 .Fn abs
 function first appeared in
 .At v6 .
-.Sh BUGS
-The absolute value of the most negative integer remains negative.
+.Sh CAVEATS
+The result of applying
+.Fn abs
+to
+.Dv INT_MIN
+is undefined.

src/lib/libc/stdlib/imaxabs.3

@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: imaxabs.3,v 1.7 2014/11/30 21:21:59 schwarze Exp $
+.\"	$OpenBSD: imaxabs.3,v 1.8 2019/01/18 07:32:17 schwarze Exp $
 .\"
-.Dd $Mdocdate: November 30 2014 $
+.Dd $Mdocdate: January 18 2019 $
 .Dt IMAXABS 3
 .Os
 .Sh NAME
@@ -39,6 +39,7 @@
 .Nd integer absolute value function
 .Sh SYNOPSIS
 .In inttypes.h
+.In stdint.h
 .Ft intmax_t
 .Fn imaxabs "intmax_t j"
 .Sh DESCRIPTION
@@ -61,5 +62,9 @@ The
 .Fn imaxabs
 function conforms to
 .St -isoC-99 .
-.Sh BUGS
-The absolute value of the most negative integer remains negative.
+.Sh CAVEATS
+The result of applying
+.Fn imaxabs
+to
+.Dv INTMAX_MIN
+is undefined.

src/lib/libc/stdlib/labs.3

@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: labs.3,v 1.16 2017/08/01 14:57:02 schwarze Exp $
+.\"	$OpenBSD: labs.3,v 1.17 2019/01/18 07:32:17 schwarze Exp $
 .\"
-.Dd $Mdocdate: August 1 2017 $
+.Dd $Mdocdate: January 18 2019 $
 .Dt LABS 3
 .Os
 .Sh NAME
@@ -40,6 +40,7 @@
 .Nm qabs
 .Nd return the absolute value of a long integer
 .Sh SYNOPSIS
+.In limits.h
 .In stdlib.h
 .Ft long
 .Fn labs "long i"
@@ -73,5 +74,15 @@ and
 .Fn llabs
 functions conform to
 .St -isoC-99 .
-.Sh BUGS
-The absolute value of the most negative integer remains negative.
+.Sh CAVEATS
+The results of applying
+.Fn labs
+to
+.Dv LONG_MIN
+and
+.Fn llabs
+to
+.Dv LLONG_MIN
+are undefined, and
+.Fn qabs
+is not portable in the first place.