Allow parallel building in libm

libm/Makefile

@@ -102,8 +102,9 @@ endif
 $(AR_LIB_NAME): $(OBJS) $(ARCH_OBJS)
 	$(INSTALL) -d $(TOPDIR)lib
 	$(RM) $(AR_LIB_NAME)
-	$(AR) $(ARFLAGS) $(AR_LIB_NAME) $(OBJS) && \
-		$(AR) $(ARFLAGS) $(AR_LIB_NAME) $(ARCH_OBJS)
+	$(AR) $(ARFLAGS) $(AR_LIB_NAME).tmp $(OBJS)
+	$(AR) $(ARFLAGS) $(AR_LIB_NAME).tmp $(ARCH_OBJS)
+	mv $(AR_LIB_NAME).tmp $(AR_LIB_NAME)
 
 $(SO_LIB_NAME): $(AR_LIB_NAME)
 	$(RM) $(TOPDIR)lib/$(SO_FULL_NAME) $(SO_LIB_NAME).$(MAJOR_VERSION) $(SO_LIB_NAME)