Break the "bison.help: bison" dependency to avoid rebuilding bison.info.

Index: Makefile.in
--- Makefile.in.orig
+++ Makefile.in
@@ -10432,7 +10432,7 @@ $(srcdir)/$(doc_bison).info.bak: $(srcdir)/$(doc_bison
 
 doc/refcard.pdf: doc/refcard.tex
 	$(AM_V_GEN) cd doc && pdftex $(abs_top_srcdir)/doc/refcard.tex
-@CROSS_COMPILING_FALSE@$(top_srcdir)/doc/bison.help: src/bison$(EXEEXT)
+@CROSS_COMPILING_FALSE@$(top_srcdir)/doc/bison.help: #src/bison$(EXEEXT)
 @CROSS_COMPILING_FALSE@	$(AM_V_GEN)$(MKDIR_P) doc
 @CROSS_COMPILING_FALSE@	$(AM_V_at) LC_ALL=C tests/bison --version >doc/bison.help.tmp
 @CROSS_COMPILING_FALSE@	$(AM_V_at) LC_ALL=C tests/bison --help | \