A pile of x86 fixes:

  - Prevent a memory leak in ioperm which was caused by the stupid
    assumption that the exit cleanup is always called for current, which is
    not the case when fork fails after taking a reference on the ioperm
    bitmap.

  - Fix an arithmething overflow in the DMA code on 32bit systems

  - Fill gaps in the xstate copy with defaults instead of leaving them
    uninitialized

  - Revert: o"Make __X32_SYSCALL_BIT be unsigned long" as it turned out
    that existing user space fails to build.
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