Stackless issue #298: Fix a race in the build process

Kristján pointed me to another race, but now extracting the archive
members should be save.

(cherry picked from commit 61e405e)

Author: Anselm Kruis

Makefile.pre.in

@@ -716,7 +716,7 @@ $(srcdir)/Include/cpython/slp_exttype.h: $(srcdir)/Objects/typeobject.c $(srcdir
 
 $(SLP_STACKMAN_OBJS): $(SLP_STACKMAN_LIB)
 	cp $(SLP_STACKMAN_LIB) Stackless/platf/libstackman.a_$$$$ && \
-	cd Stackless/platf && $(AR) x libstackman.a_$$$$ && rm libstackman.a_$$$$
+	cd Stackless/platf && $(AR) x libstackman.a_$$$$ $(@F) && rm libstackman.a_$$$$
 
 Stackless/platf/slp_transfer.o: $(srcdir)/Stackless/platf/slp_transfer.c
 	$(CC) -c $(PY_CORE_CFLAGS) $(SLPFLAGS) -o $@ $(srcdir)/Stackless/platf/slp_transfer.c