tests/migration: Convert x86 boot block compilation script into Makefile

The x86 boot block header currently is generated with a shell script.
To better support other CPUs (e.g. aarch64), we convert the script
into Makefile. This allows us to 1) support cross-compilation easily,
and 2) avoid creating a script file for every architecture.

Note that, in the new design, the cross compiler prefix can be specified by
setting the CROSS_PREFIX in "make" command. Also to allow gcc pre-processor
to include the C-style file correctly, it also renames the
x86-a-b-bootblock.s file extension from .s to .S.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Wei Huang <wei@redhat.com>
Message-Id: <1536174934-26022-2-git-send-email-wei@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tests/migration/Makefile

@@ -0,0 +1,31 @@
+# To specify cross compiler prefix, use CROSS_PREFIX=
+#   $ make CROSS_PREFIX=x86_64-linux-gnu-
+
+override define __note
+/* This file is automatically generated from
+ * tests/migration/x86-a-b-bootblock.S, edit that and then run
+ * tests/migration/rebuild-x86-bootblock.sh to update,
+ * and then remember to send both in your patch submission.
+ */
+endef
+export __note
+
+.PHONY: all clean
+all: x86-a-b-bootblock.h
+
+x86-a-b-bootblock.h: x86.bootsect
+	echo "$$__note" > header.tmp
+	xxd -i $< | sed -e 's/.*int.*//' >> header.tmp
+	mv header.tmp $@
+
+x86.bootsect: x86.boot
+	dd if=$< of=$@ bs=256 count=2 skip=124
+
+x86.boot: x86.o
+	$(CROSS_PREFIX)objcopy -O binary $< $@
+
+x86.o: x86-a-b-bootblock.S
+	$(CROSS_PREFIX)gcc -m32 -march=i486 -c $< -o $@
+
+clean:
+	@rm -rf *.boot *.o *.bootsect