MFH r328332:
Sync libarchive with vendor.

Relevant vendor changes:
PR #893: delete dead ppmd7 alloc callbacks
PR #904: Fix archive freeing bug in bsdcat
PR #961: Fix ZIP format names
PR #962: Don't modify attributes for existing directories
when ARCHIVE_EXTRACT_NO_OVERWRITE is set
PR #964: Fix -Werror=implicit-fallthrough= for GCC 7
PR #970: zip: Allow backslash as path separator