bison.m4 breaks build on systems without Bison

[Derek Robert Price]

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I suggest calling AM_MISSING_PROG(YACC, bison -y) from bison.m4 rather
than just naively setting and substing.  Patch attached.

Derek

- --
                *8^)

Email: derek@ximbiot.com

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Index: ChangeLog
===================================================================
RCS file: /cvsroot/gnulib/gnulib/ChangeLog,v
retrieving revision 1.148
diff -u -p -r1.148 ChangeLog
--- ChangeLog   27 Apr 2004 22:11:37 -0000      1.148
+++ ChangeLog   3 May 2004 14:51:54 -0000
@@ -1,5 +1,9 @@
 2004-04-27  Derek Price  <derek@ximbiot.com>
 
+       * m4/bison.m4: Use AM_MISSING_PROG rather than a set/subst combination.
+
+2004-04-27  Derek Price  <derek@ximbiot.com>
+
        * m4/dos.m4 (gl_AC_DOS): Add Cygwin to list of Windows/DOS
        environments that accept backslashes and drive letters in paths.
 
Index: m4/bison.m4
===================================================================
RCS file: /cvsroot/gnulib/gnulib/m4/bison.m4,v
retrieving revision 1.3
diff -u -p -r1.3 bison.m4
--- m4/bison.m4 18 Apr 2004 18:12:50 -0000      1.3
+++ m4/bison.m4 3 May 2004 14:51:55 -0000
@@ -3,6 +3,5 @@
 AC_DEFUN([gl_BISON],
 [
   # getdate.y works with bison only.
-  : ${YACC='bison -y'}
-  AC_SUBST(YACC)
+  AM_MISSING_PROG(YACC, bison -y)
 ])