testapp: gen-syscall-events: use dynamic paths provided via args

testapp: gen-syscall-events: use dynamic paths provided via args

This is to try and mitigate the limitation found here:
https://bugs.lttng.org/issues/1261

Using an argument ensures that the path is not in the .rodata section of
the executable and reduces the chance that the kernel tracer incurs a
page fault when attempting to serialize the path argument.

The path is pre-faulted to mitigate the problem described in #1261.

Fixes #1261

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I6b6173ee5d8b33dcdf1cc391db9d1eafe00f90b9
Depends-on: lttng-ust: I5a800fc92e588c2a6a0e26282b0ad5f31c044479