It seems the problem is
> checking for ANSI C header files... no
which causes <stdarg.h> not to be included. Dunno what about Solaris
is nonstandard enough to fool autoconf's test, but I see that the
AC_HEADER_STDC macro tests quite a bit more than just whether the header
files exist.
Try modifying src/include/c.h so that <stddef.h> and <stdarg.h> are
included unconditionally. That's how it's done in current sources...
regards, tom lane