libdiff: Add a test for the truncation issue.

[des]

Summary

Sponsored by: Klara, Inc.

[markj]

lib/libdiff/tests/libdiff_test.c

36

You might consider using some multiple of the system page size instead. For instance, on arm64 it's possible to configure a base page size of 64KB, in which case this test is going to truncate within a page and so won't trigger SIGBUS.

55

In general you don't need to clean up files in the current directory, kyua or whatever other test runner should handle that for you I believe.