Since the codebase is as of yet inconsistent, disable per-commit style
check enforcement.

This should be turned back on once the codebase style is consistent.

Adjust pid filtering/display in runqlat

The filtering and display of pids in the runqlat tool was not correct.
Internally, the kernel keeps pid and tgid, which correspond to thread-id
and user process-id, respectively. The runqlat tool was filtering and
displaying pid instead of tgid.

Change -P and -p options to filter by tgid, and add a new option to give
a breakdown by pid (thread-id).

Update the docs with the -L option.

Fixes for clang frontend bugs and misc

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>

Even after fixing the nested union issue in the preceding commits, this
example was failing. The reason was that the kernel was filling in all
bits of the bpf_tunnel_key, which in recent kernels includes non-zero
fields such as ttl. That non-zero field would break the lookup in the
tunkey2if table, which was populated assuming all extra bytes would be
zero.

Fix it by defining a simpler key structure, and copy the required fields
out from the local variable.

Fixes: #510

Clang was up until now not able to parse nested structs or unions as a
field in the table key or leaf. Add support in the library side, as well
as python support for the exported json description.

The variable inside the if statement was unused, unliked the blocks
above and below it. Use the isa<> check instead.

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.