Introduce tprintf_comment and tprints_comment functions

Introduce tprintf_comment and tprints_comment functions

* defs.h (tprintf_comment, tprints_comment): New prototypes.
* strace.c (tvprintf): New function.
(tprintf): Use it.
(tprintf_comment, tprints_comment): New functions.
* aio.c (tprint_lio_opcode): Use tprints_comment.
* dm.c (dm_decode_dm_target_spec, dm_decode_dm_target_deps,
dm_decode_dm_name_list, dm_decode_dm_target_versions,
dm_decode_dm_target_msg, dm_decode_string, dm_known_ioctl): Likewise.
* futex.c (SYS_FUNC(futex)): Likewise.
* perf.c (print_perf_event_attr): Likewise.
* seccomp.c (decode_bpf_code): Likewise.
* util.c (printxvals, printxval_searchn, printflags64): Likewise.
* btrfs.c (print_u64, btrfs_print_key_type, btrfs_print_objectid,
print_key_value_internal): Likewise.
(btrfs_ioctl): Use tprints_comment and tprintf_comment.
* dirent.c (SYS_FUNC(getdents)): Likewise.
* dirent64.c (SYS_FUNC(getdents64)): Likewise.
* execve.c (printargc): Use tprintf_comment.
* tests/btrfs.c (btrfs_test_get_dev_stats_ioctl,
btrfs_test_features_ioctls): Update expected output.