Drop /lib32 and /lib64 from link directories and RPATH (#14875)

Extend CMAKE_PLATFORM_IMPLICIT_LINK_DIRECTORIES with these paths.  We
already have the equivalents under /usr.  Systems that have these
directories have their dynamic loaders configured already.  Do not allow
them to appear in the RPATH explicitly.
cmArchiveWrite: Handle NULL error string (#14882)

If archive_error_string returns NULL, use a placeholder string instead
of crashing.
Merge branch 'implicit-libNN-dirs' into release
Merge branch 'archive-null-error' into release