x86: Add build salt to the vDSO

The vDSO needs to have a unique build id in a similar manner
to the kernel and modules. Use the build salt macro.

Acked-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

arch/x86/entry/vdso/vdso32/note.S

@@ -4,6 +4,7 @@
  * Here we can supply some information useful to userland.
  */
 
+#include <linux/build-salt.h>
 #include <linux/version.h>
 #include <linux/elfnote.h>
 
@@ -14,6 +15,8 @@ ELFNOTE_START(Linux, 0, "a")
 	.long LINUX_VERSION_CODE
 ELFNOTE_END
 
+BUILD_SALT
+
 #ifdef CONFIG_XEN
 /*
  * Add a special note telling glibc's dynamic linker a fake hardware