- turns out `pahole` for `vmlinux` can take multiple gigabytes of RAM to run successfully
- I can't simply decide based on available RAM, as that would make .config hashes mismatch
- thus, introduce:
- default is to enable BTF; if on low-ram host, error out unless KERNEL_BTF=yes is passed
- if KERNEL_BTF=no is passed, the BTF debug info is always disabled
- if KERNEL_BTF=yes is passed, then a warning is produced, but BTF is still enabled
- the magic number "6451 MiB" was determined empirically (and is probably bs)
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