Refactor flex and bison make rules

Numerous flex and bison make rules have appeared in the source tree
over time, and they are all virtually identical, so we can replace
them by pattern rules with some variables for customization.

Users of pgxs will also be able to benefit from this.

src/backend/parser/Makefile

@@ -17,8 +17,6 @@ OBJS= analyze.o gram.o keywords.o kwlookup.o parser.o \
       parse_expr.o parse_func.o parse_node.o parse_oper.o parse_param.o \
       parse_relation.o parse_target.o parse_type.o parse_utilcmd.o scansup.o
 
-FLEXFLAGS = -CF -b -p -p
-
 include $(top_srcdir)/src/backend/common.mk
 
 
@@ -40,22 +38,12 @@ endif
 
 gram.h: gram.c ;
 
-gram.c: gram.y
-	$(PERL) $(srcdir)/check_keywords.pl $< $(top_srcdir)/src/include/parser/kwlist.h
-ifdef BISON
-	$(BISON) -d $(BISONFLAGS) -o $@ $<
-else
-	@$(missing) bison $< $@
-endif
+gram.c: BISONFLAGS += -d
+gram.c: BISON_CHECK_CMD = $(PERL) $(srcdir)/check_keywords.pl $< $(top_srcdir)/src/include/parser/kwlist.h
 
 
-scan.c: scan.l
-ifdef FLEX
-	$(FLEX) $(FLEXFLAGS) -o'$@' $<
-	@if [ `wc -l <lex.backup` -eq 1 ]; then rm lex.backup; else echo "Scanner requires backup, see lex.backup."; exit 1; fi
-else
-	@$(missing) flex $< $@
-endif
+scan.c: FLEXFLAGS = -CF -p -p
+scan.c: FLEX_NO_BACKUP=yes
 
 
 # Force these dependencies to be known even without dependency info built: