[PATCH v6 15/16] perf tools: add feature header record to pipe-mode

Add header record types to pipe-mode, reusing the functions used in file-mode and leveraging the new struct feat_fd. For alignment, check that synthesized events don't exceed pagesize. Add the perf_event__synthesize_feature event call back to process the new header records. Before this patch:

[PATCH v6 15/16] perf tools: add feature header record to pipe-mode

Add header record types to pipe-mode, reusing the functions used in file-mode and leveraging the new struct feat_fd. For alignment, check that synthesized events don't exceed pagesize. Add the perf_event__synthesize_feature event call back to process the new header records. Before this patch: