On a new AIX 7.2 machine with the latest bison, I get these errors 
building kerberos 1.18.2 :


bison -y  getdate.y
getdate.y:191.25-28: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   191 | %type   <Number>        tDAY tDAYZONE tMINUTE_UNIT tMONTH 
tMONTH_UNIT
       |                         ^~~~
getdate.y:191.30-37: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   191 | %type   <Number>        tDAY tDAYZONE tMINUTE_UNIT tMONTH 
tMONTH_UNIT
       |                              ^~~~~~~~
getdate.y:191.39-50: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   191 | %type   <Number>        tDAY tDAYZONE tMINUTE_UNIT tMONTH 
tMONTH_UNIT
       |                                       ^~~~~~~~~~~~
getdate.y:191.52-57: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   191 | %type   <Number>        tDAY tDAYZONE tMINUTE_UNIT tMONTH 
tMONTH_UNIT
       | ^~~~~~
getdate.y:191.59-69: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   191 | %type   <Number>        tDAY tDAYZONE tMINUTE_UNIT tMONTH 
tMONTH_UNIT
| ^~~~~~~~~~~
getdate.y:192.25-33: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   192 | %type   <Number>        tSEC_UNIT tSNUMBER tUNUMBER tZONE
       |                         ^~~~~~~~~
getdate.y:192.35-42: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   192 | %type   <Number>        tSEC_UNIT tSNUMBER tUNUMBER tZONE
       |                                   ^~~~~~~~
getdate.y:192.44-51: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   192 | %type   <Number>        tSEC_UNIT tSNUMBER tUNUMBER tZONE
       |                                            ^~~~~~~~
getdate.y:192.53-57: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   192 | %type   <Number>        tSEC_UNIT tSNUMBER tUNUMBER tZONE
       | ^~~~~
getdate.y:193.25-33: warning: POSIX yacc reserves %type to nonterminals 
[-Wyacc]
   193 | %type   <Meridian>      tMERIDIAN o_merid
       |                         ^~~~~~~~~
getdate.y: warning: 4 shift/reduce conflicts [-Wconflicts-sr]
gmake[2]: *** [<builtin>: getdate.c] Broken pipe
gmake[2]: Leaving directory 
'/monsoon1/users/normg/gs353/slow9/kerberos/src/kadmin/cli'
gmake[1]: *** [Makefile:865: all-recurse] Error 1
gmake[1]: Leaving directory 
'/monsoon1/users/normg/gs353/slow9/kerberos/src/kadmin'
gmake: *** [Makefile:1546: all-recurse] Error 1
Build failed

normg@monsoon>bison --version
bison (GNU Bison) 3.5.1
Written by Robert Corbett and Richard Stallman.

Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Older versions of bison do not show this problem (bison 3.0.4 works fine).

Norm Green