[PATCH 0/3] [v2] x86: compat_siginfo fixes and build-time tests

[Dave Hansen]

Changes from v1:
 * lots of style fixups to the MPX selftests.  No
   Functional changes.

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We have not been updating the x86 compat_siginfo when updating the
generic one.  These patches fix the issue, and then add a bunch
of build-time checks to try to avoid this happening again in the
future (suggested by Ingo).