syz-extract: Support KLEAF builds

[r0xen]

Currently syz-extract doesn't work against a KLEAF compiled kernel which uses hermetic builds. Even compiling a kernel with --config=fast to have local cache it's not enough when passing it to syz-extract as sourcedir or builddir.

Do you already have a workaround for this?

[dvyukov]

Hi @r0xen,

It's the first time I hear about KLEAF. So, no, there are no workarounds and I don't understand what exactly is the problem and how hard it is to resolve.