unix: generate GOARCH specific zsysctl files on OpenBSD

Since CL 10087 build tags for GOOS and GOARCH are emitted by
mksysctl_openbsd.go but the generated file is always written to
zsysctl_openbsd.go.

Adjust mkall.sh to write to GOOS/GOARCH specific files and create a
zsysctl_openbsd_${GOARCH}.go file for each GOARCH supported on openbsd.

Change-Id: Id2a7b2815081f024de0ca87ba870a672bab32d24
Reviewed-on: https://go-review.googlesource.com/68870
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/mkall.sh

@@ -142,7 +142,6 @@ openbsd_386)
 	mkerrors="$mkerrors -m32"
 	mksyscall="./mksyscall.pl -l32 -openbsd"
 	mksysctl="./mksysctl_openbsd.pl"
-	zsysctl="zsysctl_openbsd.go"
 	mksysnum="curl -s 'http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/syscalls.master' | ./mksysnum_openbsd.pl"
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs"
 	;;
@@ -150,7 +149,6 @@ openbsd_amd64)
 	mkerrors="$mkerrors -m64"
 	mksyscall="./mksyscall.pl -openbsd"
 	mksysctl="./mksysctl_openbsd.pl"
-	zsysctl="zsysctl_openbsd.go"
 	mksysnum="curl -s 'http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/syscalls.master' | ./mksysnum_openbsd.pl"
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs"
 	;;
@@ -158,7 +156,6 @@ openbsd_arm)
 	mkerrors="$mkerrors"
 	mksyscall="./mksyscall.pl -l32 -openbsd -arm"
 	mksysctl="./mksysctl_openbsd.pl"
-	zsysctl="zsysctl_openbsd.go"
 	mksysnum="curl -s 'http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/sys/kern/syscalls.master' | ./mksysnum_openbsd.pl"
 	# Let the type of C char be signed for making the bare syscall
 	# API consistent across platforms.