threadsnoop: use `strftime` instead of `elapsed` #17

Job	Run time
build_test (LLVM 10 Debug, Debug, .#bpftrace-llvm10, probe.kprobe_offset_fail_size,usdt.usdt prob...	13m 55s
build_test (LLVM 10 Release, Release, .#bpftrace-llvm10, probe.kprobe_offset_fail_size,usdt.usdt ...	10m 4s
clang-format	0s
build_test (LLVM 10 Clang Debug, Debug, .#bpftrace-llvm10, clang, clang++, probe.kprobe_offset_fa...	9m 53s
build_test (LLVM 11 Debug, Debug, .#bpftrace-llvm11, probe.kprobe_offset_fail_size,usdt.usdt prob...	10m 42s
build_test (LLVM 11 Release, Release, .#bpftrace-llvm11, probe.kprobe_offset_fail_size,usdt.usdt ...	9m 52s
build_test (LLVM 12 Release, Release, .#bpftrace-llvm12, probe.kprobe_offset_fail_size,usdt.usdt ...	10m 0s
build_test (LLVM 13 Release, Release, .#bpftrace-llvm13, probe.kprobe_offset_fail_size,usdt.usdt ...	9m 49s
build_test (LLVM 14 Release, Release, .#bpftrace-llvm14, probe.kprobe_offset_fail_size,usdt.usdt ...	9m 54s
build_test (LLVM 15 Release, Release, .#bpftrace-llvm15, probe.kprobe_offset_fail_size,usdt.usdt ...	12m 40s
build_test (LLVM 16 Release, Release, .#bpftrace-llvm16, probe.kprobe_offset_fail_size,usdt.usdt ...	12m 35s
build_test (LLVM 17 Release, Release, .#bpftrace-llvm17, probe.kprobe_offset_fail_size,usdt.usdt ...	12m 43s
build_test (Memleak test (LLVM 11 Debug), Debug, .#bpftrace-llvm11, 1, 0)	9m 11s
build_test (Memleak test (LLVM 11 Release), Release, .#bpftrace-llvm11, 1, 0)	8m 2s
irc	0s
	2h 19m 20s

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