CL 32796 changes the SIGPIPE behaviour for c-archive and c-shared
programs. Add it to go1.8.txt.

Change-Id: I31200187033349c642965a4bb077bcc77d5329a3
Reviewed-on: https://go-review.googlesource.com/33397Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>