Uncomment run-time objcode alignment check.

Uncomment run-time objcode alignment check.

This should now work thanks to the changes in
28b119ee3da0f4b14cb87e638794d22843778cda ("make sure all programs are
8-byte aligned").  This commit is a follow-up to
ec99fe8ecb412e49e8e981246eb62ca46b32754b ("Add FIXMEs about misaligned
objcode-metas.").

* libguile/objcodes.c (scm_c_make_objcode_slice): Uncomment assertion
  that checks for proper alignment of PTR.

* module/language/assembly/compile-bytecode.scm (write-bytecode): Update
  comment about META's alignment.