x86-urgent-2020-05-24

  - Unbreak stack dumps for inactive tasks by interpreting the special
    first frame left by __switch_to_asm() correctly. The recent change not
    to skip the first frame so ORC and frame unwinder behave in the same
    way caused all entries to be unreliable, i.e. prepended with '?'.

  - Use cpumask_available() instead of an implicit NULL check of a
    cpumask_var_t in mmio trace to prevent a Clang build warning