perf/core cleanups: (Arnaldo Carvalho de Melo)

. Introduce new header files out of the hodge-podge that util/util.h
  became, trying to disentangle the includes hell that all C projects
  end up growing. This should help in build times, as changes to
  seemingly unrelated files (util.h included tons of headers) won't
  trigger a rebuild of most object files.

. Use equivalent facilities found in the kernel source code base
  originated tools/include/ header files, such as __stringify(),
  ARRAY_SIZE, that has extra checks (__must_be_array()), etc.

. For that get some more files from the kernel sources, like
  include/linux/bug.h, some just with the bits needed at this time.

. Use the headers where facilities declared in them are used, such
  as PRIxu(32,64) macros (inttypes.h), errno defines (errno.h), etc.

. Remove various leftovers from the initial code base we copied from
  git.git: FLEX_ARRAY, etc.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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