cc: Handle nested functions correctly when resolving symbols
cc: Handle nested functions correctly when resolving symbols

`ProcSyms::Module::find_addr` incorrectly resolves symbols when
functions are nested in each other. Specifically, this was discovered
with libpthread, where there are multiple symbols for `write`,
where `write_nocancel` is strictly nested inside `write`. Fix by
explicitly going backward until we reach a matching symbol -- see
details in `ProcSyms::Module::find_addr` comments.

iovisor/bcc,tuxology/bcc,shodoco/bcc,mcaleavya/bcc,iovisor/bcc,tuxology/bcc,shodoco/bcc,mcaleavya/bcc,mcaleavya/bcc,brendangregg/bcc,shodoco/bcc,tuxology/bcc,romain-intel/bcc,shodoco/bcc,brendangregg/bcc,brendangregg/bcc,shodoco/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,romain-intel/bcc,romain-intel/bcc,tuxology/bcc,romain-intel/bcc,iovisor/bcc,romain-intel/bcc,brendangregg/bcc,iovisor/bcc,mcaleavya/bcc,mcaleavya/bcc