Fix BSD -rpath parameter

For BSD systems, Configure adds a shared_ldflags including a reference
to the Makefile variable LIBRPATH, but since it must be passed down to
Makefile.shared, care must be taken so the value of LIBRPATH doesn't
get expanded too early, or it ends up giving an empty string.
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>

Configure

@@ -1737,7 +1737,7 @@ if ($target =~ /\-icc$/)	# Intel C compiler
 # linker only when --prefix is not /usr.
 if ($target =~ /^BSD\-/)
 	{
-	$shared_ldflag.=" -Wl,-rpath,\$(LIBRPATH)" if ($prefix !~ m|^/usr[/]*$|);
+	$shared_ldflag.=" -Wl,-rpath,\$\$(LIBRPATH)" if ($prefix !~ m|^/usr[/]*$|);
 	}
 
 if ($sys_id ne "")