Log Message:
Problem: Dirmngr depends on pth. With an explicit buildlink to pth, the
package builds and works correctly. This approach was taken prior to
this change. The is a problem because  pth installs pthread.h in
${LOCALBASE}/include. This causes problems for things like Ada tasking
that depend on native pthreads when also linking against libraries in
pkgsrc (eg., gmp).

This change solve the problem by building a static pth library locally
and linking against it.