do not use pthreads on hpux (broken, hardly useful).

For reference, I get the following when starting a version compiled with it:
Pthread internal error: message: __libc_reinit() failed, file: /ux/core/kern/pthreads/pthread.c, line: 1093
Return Pointer is 0xc0e29273
Quit


git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@14227 b3059339-0415-0410-9bf9-f77b7e298cf2

configure

@@ -2678,6 +2678,8 @@ int main(void) { pthread_t tid; return pthread_create (&tid, 0, func, 0) == 0 ?
 EOF
 if mingw32 ; then
   _ld_pthread=''
+elif hpux ; then
+  _ld_pthread=''
 elif ( cc_check && $TMPO ) ; then              # QNX
   _ld_pthread=''
 elif ( cc_check -lpthread && $TMPO ) ; then