Use the PTHREAD_XXX variables to set up the linking, otherwise libGL.so isn't
linked with libpthread.so under Linux, and so things that link with libGL.so
but don't themselves use threads are likely to not link themselves, failing to
resolve pthread_getspecific, pthread_once, pthread_key_create and
pthread_setspecific.
There should be no change on NetBSD platforms, but there is change on other
platforms, notably Linux. Bump PKGREVISION to communicate that.
Should fix PR36207, does fix Linux build of glx-utils, and allows mission
critical software like "bzflag" to build under Linux.
fc9e05c6f4