[krbdev.mit.edu #3887] krb5-config lists too many libraries

[Ken Raeburn via RT]

Now -lkeyutils is added on Linux, if the krb5 code was built with the keyring support.  This 
could cause applications to needlessly depend on the keyutils library, making them unportable 
to another Linux box without the keyutils library but with the same krb5 library (aside from 
having been compiled without the keyutils dependency).