perf annotate: Start supporting cross arch annotation

perf annotate: Start supporting cross arch annotation

Introduce a 'struct arch', where arch specific stuff will live, starting
with objdump's choice of comment delimitation character, that is '#' in
x86 while a ';' in arm.

This has some bits and pieces from a patch submitted by Ravi.

Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Chris Riyder <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kim Phillips <[email protected]>
Cc: Markus Trippelsdorf <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Naveen N. Rao <[email protected]>
Cc: Pawel Moll <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Taeung Song <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>