o/build/mkpayload: port to llvm-objcopy

GNU and LLVM objcopy have some material differences in how they work.
LLVM is able to automatically assign VMAs, but needs --set-section-flags
for it. Use that and drop all the explicit VMAs.
Also with the new toolchain cc.objcopy_excutable is not populated, so we
need to get the executable path using the new action-based way.

Currently contains a hack to force static on to get our custom toolchain
for both host and cross-builds as GNU objcopy is not compatible.

Change-Id: I0a5ef1cbeb3f94326a2cef099c23c046df166bdd
Reviewed-on: https://review.monogon.dev/c/monogon/+/4214
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/build/mkpayload/mkpayload.go b/osbase/build/mkpayload/mkpayload.go
index c1433f3..f486134 100644
--- a/osbase/build/mkpayload/mkpayload.go
+++ b/osbase/build/mkpayload/mkpayload.go
@@ -39,15 +39,14 @@
 	// as command line parameters.
 	sections = map[string]struct {
 		descr    string
-		vma      string
 		required bool
 		file     *string
 	}{
-		"linux":   {"Linux kernel image", "0x2000000", true, nil},
-		"initrd":  {"initramfs", "0x5000000", false, nil},
-		"osrel":   {"OS release file in text format", "0x20000", false, nil},
-		"cmdline": {"a file containting additional kernel command line parameters", "0x30000", false, nil},
-		"splash":  {"a splash screen image in BMP format", "0x40000", false, nil},
+		"linux":   {"Linux kernel image", true, nil},
+		"initrd":  {"initramfs", false, nil},
+		"osrel":   {"OS release file in text format", false, nil},
+		"cmdline": {"a file containting additional kernel command line parameters", false, nil},
+		"splash":  {"a splash screen image in BMP format", false, nil},
 	}
 	initrdList      stringList
 	objcopy         = flag.String("objcopy", "", "objcopy executable")
@@ -151,7 +150,7 @@
 		if *c.file != "" {
 			args = append(args, []string{
 				"--add-section", fmt.Sprintf(".%s=%s", name, *c.file),
-				"--change-section-vma", fmt.Sprintf(".%s=%s", name, c.vma),
+				fmt.Sprintf("--set-section-flags=.%s=data", name),
 			}...)
 		}
 	}