Powerpc support v2

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

__per_cpu_start has a different address on each architecture. Instead,
use a arch-unique symbol for the test.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

Basic support for building on powerpc. Tested on ppc64le.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

cc/clang: Use positional arguments for diagnostic messages

Lua tooling improvements

updated opensnoop to use bpf_perf_output

[WIP] Native implementation for USDT probes

To avoid exposing the implementation of new/delete of the Argument
class, move it out of the header file. This also requires making private
the std::string members, so that they cannot be assigned to directly.
Let the ArgumentParser assign to them as a friend, and expose const
functions to access them as const only from the client.

Also, convert non-const reference usages to pass-by-pointer.

bpf: Wrap `bcc_procutils_which_so` as `BPF.find_library`

This class method was being used outside of the BPF class in the
`tracer` and `usdt` tools.

Explicitly list the libelf runtime dependency

Add libelf-dev to Ubuntu build deps

This was required on a Debian system, but in lieu of instructions for that distribution, and as Debian users will follow Ubuntu, would you consider verifying it on Ubuntu and accepting this PR?

[RFC] Remove all dependencies on external binaries