kleaf: kernel_build() generates vmlinux.symvers or Module.symvers accordingly.

This is so that, on 6.13, we no longer rely on Kbuild to generate
vmlinux.symvers (for GKI) or Module.symvers (for device kernel_build())
for us.

We still need Kbuild to generate modules-only.symvers for device
kernel_build(), though.

Bug: 402231876
Change-Id: I104653c7f33971a1befb974153f7ab69b5997f0c
1 file changed