[krbdev.mit.edu #3912] krb5-1.5: fix warnings in util/support/

[Public Submitter via RT]

Fixes some compiler warnings:
# threads.c: In function 'krb5int_thread_support_init':
# threads.c:456: warning: implicit declaration of function 
'krb5int_err_init'
# errors.c: In function 'krb5int_vset_error':
# errors.c:52: warning: passing argument 1 of 'free' discards 
qualifiers from pointer target type
# errors.c:59: warning: implicit declaration of function 'vasprintf'
# errors.c: In function 'krb5int_get_error':
# errors.c:76: warning: assignment discards qualifiers from pointer 
target type
# errors.c:80: warning: implicit declaration of function 
'krb5int_call_thread_support_init'
# errors.c:120: warning: assignment discards qualifiers from pointer 
target type
# errors.c: In function 'krb5int_clear_error':
# errors.c:146: warning: passing argument 2 of 'krb5int_free_error' 
discards qualifiers from pointer target type
#