libxxhash-dev is needed for x86_64 after recent KLP -next objtool series

After

• 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums")
• 7ae60ff0b77f ("livepatch: Add CONFIG_KLP_BUILD")
• 24ebfcd65a87 ("livepatch/klp-build: Introduce klp-build script for generating livepatch modules")

in linux-next, the libxxhash-dev package is required for x86_64 to build properly with CONFIG_LIVEPATCH=y (which is most major distributions).

error: objtool: --checksum not supported; install xxhash-devel/libxxhash-dev and recompile