Ignore zero-variadic-macro-arguments warnings from lttng-ust macros

[christophebedard]

Fixes #105

The warnings are due to the lttng-ust macros. While the relevant tracetools macros have two variants to handle tracepoints with and without arguments (see comment in tracetools.h), the lttng-ust macros do not:

#define lttng_ust_do_tracepoint(provider, name, ...)

This will be called without any variadic arguments by the tracetools _CONDITIONAL_DO_TP() macro (see tracetools.c). For example, in rough order of expansion:

// 1.
DEFINE_TRACEPOINT_NO_ARGS(
  rclcpp_executor_get_next_ready)

// 2.
_CONDITIONAL_DO_TP(rclcpp_executor_get_next_ready)

// 3.
do_tracepoint(ros2, rclcpp_executor_get_next_ready)

// 4.
lttng_ust_do_tracepoint(ros2, rclcpp_executor_get_next_ready)

Therefore, ignore the gnu-zero-variadic-macro-arguments warning with clang in tp_call.h (where lttng-ust macros are used to define tracepoint events) and in tracetools.c (where lttng-ust macros are used to trigger tracepoint events).

[christophebedard]

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

I used the CI_COMPILE_WITH_CLANG option from ci_launcher, but maybe I should've just triggered a separate ci_linux_clang_libcxx job?

[fujitatomoya]

lgtm with green CI. CI failures seem unrelated to this fix.

[christophebedard]

The jobs above show that the warnings have disappeared. Looks like there's an unrelated issue with clang/libstdc++ on RHEL.

Triggering another round of CI without CI_COMPILE_WITH_CLANG just to double check that this is fine without clang:

• Linux
• Linux-aarch64
• Linux-rhel
• Windows