Don't declare calloc() and realloc() if not necessary.

acinclude.m4

@@ -11,3 +11,50 @@ AC_DEFUN(BISON_DEFINE_FILE, [
         )`
         AC_DEFINE_UNQUOTED($1, "$ac_expanded")
 ])
+
+dnl See whether we need a declaration for a function.
+dnl BISON_NEED_DECLARATION(FUNCTION [, EXTRA-HEADER-FILES])
+AC_DEFUN(BISON_NEED_DECLARATION,
+[AC_MSG_CHECKING([whether $1 must be declared])
+AC_CACHE_VAL(bison_cv_decl_needed_$1,
+[AC_TRY_COMPILE([
+#include <stdio.h>
+#ifdef HAVE_STRING_H
+#include <string.h>
+#else
+#ifdef HAVE_STRINGS_H
+#include <strings.h>
+#endif
+#endif
+#ifdef HAVE_STDLIB_H
+#include <stdlib.h>
+#endif
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#ifndef HAVE_RINDEX
+#define rindex strrchr
+#endif
+#ifndef HAVE_INDEX
+#define index strchr
+#endif
+$2],
+[char *(*pfn) = (char *(*)) $1],
+eval "bison_cv_decl_needed_$1=no", eval "bison_cv_decl_needed_$1=yes")])
+if eval "test \"`echo '$bison_cv_decl_needed_'$1`\" = yes"; then
+  AC_MSG_RESULT(yes)
+  bison_tr_decl=NEED_DECLARATION_`echo $1 | tr 'abcdefghijklmnopqrstuvwxyz' 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'`
+  AC_DEFINE_UNQUOTED($bison_tr_decl)
+else
+  AC_MSG_RESULT(no)
+fi
+])dnl
+
+dnl Check multiple functions to see whether each needs a declaration.
+dnl BISON_NEED_DECLARATIONS(FUNCTION... [, EXTRA-HEADER-FILES])
+AC_DEFUN(BISON_NEED_DECLARATIONS,
+[for ac_func in $1
+do
+BISON_NEED_DECLARATION($ac_func, $2)
+done
+])