perf diff: Link same basic blocks among different data

The target is to compare the performance difference (cycles diff) for
the same basic blocks in different data files.

The same basic block means same function, same start address and same
end address. This patch finds the same basic blocks from different data
files and link them together and resort by the cycles diff.

 v3:
 ---
 The block stuffs are maintained by new structure 'block_hist',
 so this patch is update accordingly.

 v2:
 ---
 Since now the basic block hists is changed to per symbol,
 the patch only links the basic block hists for the same
 symbol in different data files.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1561713784-30533-6-git-send-email-yao.jin@linux.intel.com


[ sym->name is an array, not a pointer, so no need to check it for NULL, fixes de build in some distros ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>