perf buildid-list: Work better with pipe mode

In order for perf buildid-list to work with pipe-mode files, it needs to
process buildids and event attr structs.

$ perf record -o - noploop 2 | ./perf inject -b | perf buildid-list -i - -H
noploop for 2 seconds
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.084 MB - (~3678 samples) ]
0000000000000000000000000000000000000000 [kernel.kallsyms]
3a0d0629efe74a8da3eeba372cdbd74ad9b8f5d5 /usr/local/bin/noploop

The reason [kernel.kallsyms] shows a 0 build-id comes from the
way buildids are injected in the stream.

The buildid for the kernel is provided by a BUILD_ID record. The
[kernel.kallsyms] is provided by a MMAP record. There is no clean and
obvious way to link the two, unfortunately.

In regular mode, the kernel buildid is generated from reading the ELF
image or kallsyms and perf knows to associate [kernel.kallsyms] to it.
Later on, when perf processes the [kernel.kallsyms] MMAP record, it will
already have a dso for it.

So for now, make sure perf buildid-list shows the buildids for
everything but the kernel image.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1337081295-10303-6-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>