We use pkg-config where we can, which generally replaces libtool at a
  higher level and does not have the same downsides as libtool. These
  archives sit in our depends tree with no purpose and pollute the final
  bitcoin build with massive overlinking.

See here for an explanation of the various problems libtool archives can
cause:
https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Handling_Libtool_Archives