libperf event: Ensure tracing data is multiple of 8 sized

libperf event: Ensure tracing data is multiple of 8 sized

Perf's synthetic-events.c will ensure 8-byte alignment of tracing
data, writing it after a perf_record_header_tracing_data event.

Add padding to struct perf_record_header_tracing_data to make it 16-byte
rather than 12-byte sized.

Fixes: 055c67ed39887c55 ("perf tools: Move event synthesizing routines to separate .c file")
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.ibm.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Chun-Tse Shao <ctshao@google.com>
Cc: Collin Funk <collin.funk1@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Polensky <japo@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nam Cao <namcao@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20250821163820.1132977-6-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>