There are a couple of ports with bootstraps that include libpthread.so,
these need regenerating to work with this.
This includes devel/jdk (should build ok with FLAVOR=native_bootstrap
if you have an already-installed copy of jdk) and lang/rust (I'm doing
a test build where I've done make extract, then copied new libs in to
the bootstrap dir, which seems to be going ok so far - though editing
do-configure to point at copies of rustc and cargo in /usr/local/bin
will probably work too).
It might be handy to add a native_bootstrap PSEUDO_FLAVOR to lang/rust
to make it a bit easier to update in these situations.