pythongh-110429: Fix race condition in "make regen-all" (python#110433)

"make regen-pegen" now creates a temporary file called "parser.c.new"
instead of "parser.new.c". Previously, if "make clinic" was run in
parallel with "make regen-all", clinic may try but fail to open
"parser.new.c" if the temporay file was removed in the meanwhile.

Makefile.pre.in

@@ -1399,8 +1399,8 @@ regen-pegen:
 	PYTHONPATH=$(srcdir)/Tools/peg_generator $(PYTHON_FOR_REGEN) -m pegen -q c \
 		$(srcdir)/Grammar/python.gram \
 		$(srcdir)/Grammar/Tokens \
-		-o $(srcdir)/Parser/parser.new.c
-	$(UPDATE_FILE) $(srcdir)/Parser/parser.c $(srcdir)/Parser/parser.new.c
+		-o $(srcdir)/Parser/parser.c.new
+	$(UPDATE_FILE) $(srcdir)/Parser/parser.c $(srcdir)/Parser/parser.c.new
 
 .PHONY: regen-ast
 regen-ast: