pg_upgrade regression test litters the source tree with log files

In a tree in which I previously ran "make check" in contrib/pg_upgrade:

$ make -s distclean
$ git status
# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#       contrib/pg_upgrade/pg_upgrade_dump_1.log
#       contrib/pg_upgrade/pg_upgrade_dump_12912.log
#       contrib/pg_upgrade/pg_upgrade_dump_16384.log
nothing added to commit but untracked files present (use "git add" to track)

Not sure how long this has been happening.
        regards, tom lane