timeout: display signal 0 as '0' instead of 'EXIT' in verbose mode

[ChrisDryden]

I've been spending the last two days working on the timeout utility now that we have SIGPIPE handling and theres a bunch of changes required to match the newest implementation of GNU timeout. This is one of the more simple changes where there was a change to treat exit as a special case and return 0 instead of EXIT. I'm just trying to split up whatever I can since the signal handling change is going to be a bigger change.

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will improve performance by 3.51%

_{Comparing ChrisDryden:timeout-signal-0-display (74e498a) with main (0d403a4)}

Summary

⚡ 1 improved benchmark
✅ 140 untouched benchmarks
⏩ 38 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	cp_large_file[16]	371.7 µs	359.1 µs	+3.51%

Footnotes

1. 38 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[Ecordonnier]

For reference: this is done to match a change in GNU coreutils after v9.9