Change in coreboot[master]: Makefile: Add .SECONDARY

[Raul Rangel (Code Review)]

Raul Rangel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62398 )

Change subject: Makefile: Add .SECONDARY
......................................................................

Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/62398/comment/81c54021_116e813b 
PS2, Line 10: Setting .SECONDARY will prevent make from
            : deleting the files.
> ... and also breaks/prevents partial rebuild :/ […]

Can you try this out?

```
diff --git a/Makefile.inc b/Makefile.inc
index ec2d097b2dda..279f8d480f03 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -1115,6 +1115,10 @@ ifeq ($(CONFIG_INTEL_ADD_TOP_SWAP_BOOTBLOCK),y)
 TS_OPTIONS := -j $(CONFIG_INTEL_TOP_SWAP_BOOTBLOCK_SIZE)
 endif

+# coreboot.pre doesn't follow the standard Make conventions. It gets modified
+# by multiple rules, and thus we can't compute the dependencies correctly.
+$(shell rm -f $(obj)/coreboot.pre)
+
 ifneq ($(CONFIG_UPDATE_IMAGE),y)
 $(obj)/coreboot.pre: $(objcbfs)/bootblock.bin $$(prebuilt-files) $(CBFSTOOL) $(obj)/fmap.fmap $(obj)/fmap.desc
        $(CBFSTOOL) $@.tmp create -M $(obj)/fmap.fmap -r $(shell cat $(obj)/fmap.desc)
```