perf record: Do not save pathname in ./debug/.build-id directory for vmlinux

perf record: Do not save pathname in ./debug/.build-id directory for vmlinux

When perf record finishes a session, it pre-processes samples in order
to write build-id info from DSOs that had samples.

During this process it'll call map__load() for the kernel map, and it
ends up calling dso__load_vmlinux_path() which replaces dso->long_name.

But this function checks kernel's build-id before searching vmlinux path
so it'll end up with a cryptic name, the pathname for the entry in the
~/.debug cache, which can be confusing to users.

This patch adds a flag to skip the build-id check during record, so
that it'll have the original vmlinux path for the kernel dso->long_name,
not the entry in the ~/.debug cache.

Before:
  # perf record -va sleep 3
  mmap size 528384B
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.196 MB perf.data (~8545 samples) ]
  Looking at the vmlinux_path (7 entries long)
  Using /home/namhyung/.debug/.build-id/f0/6e17aa50adf4d00b88925e03775de107611551 for symbols

After:
  # perf record -va sleep 3
  mmap size 528384B
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.193 MB perf.data (~8432 samples) ]
  Looking at the vmlinux_path (7 entries long)
  Using /lib/modules/3.16.4-1-ARCH/build/vmlinux for symbols

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1415063674-17206-7-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>