Don't run pgen twice when using make -j.

Makefile.pre.in

@@ -561,9 +561,12 @@ Modules/python.o: $(srcdir)/Modules/python.c
 
 $(IO_OBJS): $(IO_H)
 
-$(GRAMMAR_H) $(GRAMMAR_C): $(PGEN) $(GRAMMAR_INPUT)
+# Use a stamp file to prevent make -j invoking pgen twice
+$(GRAMMAR_H) $(GRAMMAR_C): Parser/pgen.stamp
+Parser/pgen.stamp: $(PGEN) $(GRAMMAR_INPUT)
 		-@$(INSTALL) -d Include
 		-$(PGEN) $(GRAMMAR_INPUT) $(GRAMMAR_H) $(GRAMMAR_C)
+		-touch Parser/pgen.stamp
 
 $(PGEN):	$(PGENOBJS)
 		$(CC) $(OPT) $(PY_LDFLAGS) $(PGENOBJS) $(LIBS) -o $(PGEN)
@@ -1197,7 +1200,7 @@ profile-removal:
 
 clobber: clean profile-removal
 	-rm -f $(BUILDPYTHON) $(PGEN) $(LIBRARY) $(LDLIBRARY) $(DLLLIBRARY) \
-		tags TAGS \
+		tags TAGS Parser/pgen.stamp \
 		config.cache config.log pyconfig.h Modules/config.c
 	-rm -rf build platform
 	-rm -rf $(PYTHONFRAMEWORKDIR)

Misc/NEWS

@@ -215,6 +215,11 @@ Tests
 
 - Issue #8687: provide a test suite for sched.py module.
 
+Build
+-----
+
+- Don't run pgen twice when using make -j.
+
 
 What's New in Python 3.2 Alpha 1?
 =================================