install/54835: miniroot install.sub uses sh(1) function not enabled with SMALL

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

>Number:         54835
>Category:       install
>Synopsis:       miniroot install.sub uses sh(1) function not enabled with SMALL
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jan 05 16:00:00 +0000 2020
>Originator:     Izumi Tsutsui
>Release:        NetBSD 9.0_RC1
>Organization:
>Environment:
NetBSD 9.0_RC1 (INSTALL) #0: Wed Nov 27 16:14:52 UTC 2019
  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/sun3/compile/INSTALL
Architecture: m68k
Machine: sun3, but affects all miniroot ports?
>Description:
NetBSD/sun3 9.0_RC1 miniroot script emits the following error message:
---
Installing boot block...
File system:         /dev/rsd0a
File system type:    ffs (blocksize 8192, needswap 0)
Primary bootstrap:   bootxx
Secondary bootstrap: ufsboot
Bootstrap start sector: 1
Bootstrap byte count:   6740
Bootstrap block table:  118 entries of 8192 bytes available, 3 used: 6752 6768 2818
Writing bootstrap
done.
[: SMALL test, no fallback usage
Syncing disks...done.
Umounting filesystems... /mnt/usr /mnt Done.
---

"[: SMALL test, no fallback usage" is comes from the following line:
https://nxr.netbsd.org/xref/src/distrib/miniroot/install.sub?r=1.49#1534
---
   1534 	if [ ! \( -f $_fstab -a -s $_fstab \) ]; then
   1535 		echo "fstab empty" > /dev/tty
   1536 		return
   1537 	fi
---
# if [ ! \( -f /tmp/fstab.shadow -a -s /tmp/fstab.shadow \) ] ; then
>  echo "fstab empty"
> fi
[: SMALL test, no fallback usage
# 
---

It works on non-SMALL sh(1):
---
$ if [ ! \( -f /tmp/fstab.shadow -a -s /tmp/fstab.shadow \) ] ; then
>  echo "fstab empty"
> fi
fstab empty
$ 
---

>How-To-Repeat:
Install NetBSD 9.0_RC1 via miniroot.

>Fix:
Fix install.sub script or sh(1) SMALL?

---
Izumi Tsutsui