termcap.small: Don't use -o pipefail.

The command to generate termcap.small doesn't use any pipes, so this
option is not needed. Using it also breaks cross-building on hosts
where /bin/sh does not support pipefail such as Linux hosts where
/bin/sh is dash.

Reviewed by: sobomax, imp
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D37865