Move the build rule for vmlinux.a to a separate file in preparation for supporting distributed builds with Clang ThinLTO. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Tested-by: Rong Xu <xur@google.com> Tested-by: Piotr Gorski <piotrgorski@cachyos.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Rong Xu <xur@google.com> Link: https://patch.msgid.link/20260529185347.2418373-2-xur@google.com [nathan: Squash in forward fix from Rong around '--thin' to $(AR) https://patch.msgid.link/20260529185347.2418373-3-xur@google.com] Signed-off-by: Nathan Chancellor <nathan@kernel.org>