perf/core improvements and fixes:

User visible:

- We should not use the current value of the kernel.perf_event_max_stack as the
  default value for --max-stack in tools that can process perf.data files, they
  will only match if that sysctl wasn't changed from its default value at the
  time the perf.data file was recorded, fix it.

  This fixes a bug where a 'perf record -a --call-graph dwarf ; perf report'
  produces a glibc invalid free backtrace (Arnaldo Carvalho de Melo)

- Provide a better warning when running 'perf trace' on a system where the
  kernel.kptr_restrict is set to 1, similar to the one produced by 'perf record',
  noticed on ubuntu 16.04 where this is the default kptr_restrict setting.
  (Arnaldo Carvalho de Melo)

- Fix ordering of instructions in the annotation code, noticed when annotating
  ARM binaries, now that table is auto-ordered at first use, to avoid more such
  problems (Chris Ryder)

- Set buildid dir under symfs when --symfs is provided (He Kuang)

- Fix the 'exit_group()' syscall output in 'perf trace' (Arnaldo Carvalho de Melo)

- Only auto set call-graph to "dwarf" in 'perf trace' when syscalls are being
  traced (Arnaldo Carvalho de Melo)

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