[krbdev.mit.edu #3358] krb5 doesn't build when pthread_mutexattr_setrobust_np is defined but not declared

[Ken Raeburn via RT]

I used pthread_mutexattr_setrobust_np as a weak-reference test to see  
if the pthread code was loaded on Solaris.  With the more detailed  
tests we do now, the test for that function can probably just go away  
now....

Ken