Recent libcap's assume -lpthread is available. There are some environments where this is not the case. We should restructure things so this support is optional. Specifically, this refers to libpsx building. How libpsx relates to libpthread is summarized here: https://sites.google.com/site/fullycapable/who-ordered-libpsx
https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=24375fb114e6a78aa3ca6907399b8601d1db6f36