Disable open[at] bitwise enum in default build

Disable open[at] bitwise enum in default build

Only generate the bitwise enumerations when
CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM is enabled, so the default build
does not generate traces which lead to warnings when viewed with
babeltrace 1.x and babeltrace 2 with default options.

Original commit:

  commit c8dfb72431505d5f01a6f090f3f7427d9ca6fe94
  Author: Geneviève Bastien <gbastien@versatic.net>
  Date:   Wed Mar 11 12:33:04 2020 -0400

    syscalls: Make the flags and mode fields of open[at] enumerations

Use the non-override system call tracing implementation when the enum is
not used.

Change-Id: I2dbebe56eaba6186843dab20264d3378962c7d30
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>