Derive Default for SourceLocation #350

Job	Run time
Linux (nightly)	2m 35s
Linux (nightly, --features dummy_match_byte)	2m 30s
Linux (nightly, --features malloc_size_of)	2m 35s
Linux (beta)	33s
Linux (beta, --features dummy_match_byte)	34s
Linux (beta, --features malloc_size_of)	37s
Linux (stable)	32s
Linux (stable, --features dummy_match_byte)	37s
Linux (stable, --features malloc_size_of)	32s
Linux (1.63.0)	2m 54s
Linux (1.63.0, --features dummy_match_byte)	2m 51s
Linux (1.63.0, --features malloc_size_of)	2m 51s
Linux (nightly, --features bench)	6m 3s
Linux (nightly, --features bench,dummy_match_byte)	6m 3s
Result	1s
	31m 48s

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