sparc: add -m64 when building vmlinux.lds

David Miller noticed that the build of vmlinux.lds
failed to use the -m64 specifier.
This caused the build to break with a bi-arch gcc with
unified headers.

Add the -m64 option to CPPFLAGS_vmlinux.lds so we
have the correct defines available when building
vmliux.lds.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

arch/sparc64/Makefile

@@ -9,7 +9,9 @@
 
 CHECKFLAGS	+= -D__sparc__ -D__sparc_v9__ -m64
 
-CPPFLAGS_vmlinux.lds += -Usparc
+# Undefine sparc when processing vmlinux.lds - it is used
+# And teach CPP we are doing 64 bit builds (for this case)
+CPPFLAGS_vmlinux.lds += -m64 -Usparc
 
 LDFLAGS		:= -m elf64_sparc