Hi,
Please comments and suggestions for attached patch.
I feel this issue should be fixed before 2012Q1 branch.
1. FreeBSD/NetBSD/DragonFly has pthread stubs in libc,
so no need to link with pthread library (THREAD_LIBS=""),
only selftest with pthread will require it (BASE_THREAD_LIBS).
2. Treat OpenBSD same as Linux, set weak ref to pthread_*.
(phtread_* will be never used unless libxml2 will be used with pthread)
3. NetBSD<4.99.36 does not have pthread_equal stubs in libc,
so set weak ref for it.
4. Others will be linked with pthread library.
For other platfoms (Mac OS X, Solaris, and so on) probably could be
treated same as FreeBSD/NetBSD/DragonFly or Linux/OpenBSD,
but I don't know about the status of such platforms.