Implement lbr-as-callgraph v9

[Andi Kleen]

[Forward ported to latest tip/perf/core]
[Even more review feedback and some bugs addressed.]
[Only port to changes in perf/core. No other changes.]
[Rebase to latest perf/core]
[Another rebase. No changes]

This patchkit implements lbr-as-callgraphs in per freport,
as an alternative way to present LBR information.

Current perf report does a histogram over the branch edges,
which is useful to look at basic blocks, but doesn't tell
you anything about the larger control flow behaviour.

This patchkit adds a new option --branch-history that
adds the branch paths to the callgraph history instead.

This allows to reason about individual branch paths leading
to specific samples.

Also available at
git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc perf/lbr-callgraph4

v2:
- rebased on perf/core
- fix various issues
- rename the option to --branch-history
- various fixes to display the information more concise
v3:
- White space changes
- Consolidate some patches
- Update some descriptions
v4:
- Fix various display problems
- Unknown srcline is now printed as symbol+offset
- Refactor some code to address review feedback
- Merge with latest tip
- Fix missing srcline display in stdio hist output.
v5:
- Rename functions
- Fix gtk build problem
- Fix crash without -g
- Improve error messages
- Improve srcline display in various ways
v6:
- Port to latest perf/core
v7:
- Really port to latest perf/core
v8:
- Rebased on 3.16-rc1
v9: 
- Forward ported to latest tip/perf/core

Example output:

    % perf record -b -g ./tsrc/tcall
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.044 MB perf.data (~1923 samples) ]
    % perf report --branch-history
    ...
        54.91%  tcall.c:6  [.] f2                      tcall
                |
                |--65.53%-- f2 tcall.c:5
                |          |
                |          |--70.83%-- f1 tcall.c:11
                |          |          f1 tcall.c:10
                |          |          main tcall.c:18
                |          |          main tcall.c:18
                |          |          main tcall.c:17
                |          |          main tcall.c:17
                |          |          f1 tcall.c:13
                |          |          f1 tcall.c:13
                |          |          f2 tcall.c:7
                |          |          f2 tcall.c:5
                |          |          f1 tcall.c:12
                |          |          f1 tcall.c:12
                |          |          f2 tcall.c:7
                |          |          f2 tcall.c:5
                |          |          f1 tcall.c:11


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