kbuild: link vmlinux only once for CONFIG_TRIM_UNUSED_KSYMS (2nd attempt)

If CONFIG_TRIM_UNUSED_KSYMS is enabled and the kernel is built from
a pristine state, the vmlinux is linked twice.

Commit 3fdc7d3f ("kbuild: link vmlinux only once for
CONFIG_TRIM_UNUSED_KSYMS") explains why this happens, but it did not fix
the issue at all.

Now I realized I had applied a wrong patch.

In v1 patch [1], the autoksyms_recursive target correctly recurses to
"$(MAKE) -f $(srctree)/Makefile autoksyms_recursive".

In v2 patch [2], I accidentally dropped the diff line, and it recurses to
"$(MAKE) -f $(srctree)/Makefile vmlinux".

Restore the code I intended in v1.

[1]: https://lore.kernel.org/linux-kbuild/1521045861-22418-8-git-send-email-yamada.masahiro@socionext.com/
[2]: https://lore.kernel.org/linux-kbuild/1521166725-24157-8-git-send-email-yamada.masahiro@socionext.com/



Fixes: 3fdc7d3f ("kbuild: link vmlinux only once for CONFIG_TRIM_UNUSED_KSYMS")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>