kbuild: refactor final link of sparc32

sparc32 uses an additional final link to support btfix.
Introduce a new set of exported variables in the top-level Makefile
to make the extra linking step simpler.

sparc32 has hardcoded knowledge of kallsyms support. This fix
include support for EXTRA_KALLSYM_PASS=1.
The ugly part is that it is hardcoded in the arch/sparc/boot
Makefile.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/Makefile b/Makefile
index 06aff74..7ea0c07 100644
--- a/Makefile
+++ b/Makefile
@@ -723,6 +723,11 @@
 libs-y2		:= $(patsubst %/, %/built-in.o, $(libs-y))
 libs-y		:= $(libs-y1) $(libs-y2)
 
+# externally visible symbols
+export KBUILD_VMLINUX_INIT := $(head-y) $(init-y)
+export KBUILD_VMLINUX_MAIN := $(core-y) $(libs-y) $(drivers-y) $(net-y)
+export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
+
 # Build vmlinux
 # ---------------------------------------------------------------------------
 # vmlinux is built from the objects selected by $(vmlinux-init) and