Changes

callstack: Add PID to called functions
The function created from the segment store methods should also contain 
the PID, since this data is necessary to resolve the function name.
Also, the name of a function now tries to resolve the symbol instead of 
returning the symbol address as a string.
Change-Id: I2d8a15a84470e86b688710dd598c1a4c2695e6cf Signed-off-by:
Geneviève Bastien <gbastien+lttng@versatic.net> Reviewed-on:
https://git.eclipse.org/r/146754 Tested-by: CI Bot Reviewed-by: Matthew
Khouzam <matthew.khouzam@ericsson.com> Reviewed-on:
https://git.eclipse.org/r/146824