Update libarchive to git 2d9156bb3ad92c43c1e81546f4a2c21549ba248f
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