Add support for DW_LNCT_LLVM_source #479

Job	Run time
build (ubuntu-latest, stable)	47s
build (ubuntu-latest, beta)	51s
build (ubuntu-latest, nightly)	47s
build (stable, macOS-latest)	41s
msrv	1m 46s
Build fuzz targets	1m 9s
features	3m 2s
msrv-read	1m 43s
bench	1m 16s
coverage	1m 4s
cross (i686-unknown-linux-gnu)	1m 0s
cross (powerpc64-unknown-linux-gnu)	56s
doc	23s
rustfmt	5s
Run `debug_abbrev` fuzz target	5m 6s
Run `debug_aranges` fuzz target	5m 11s
Run `debug_info` fuzz target	5m 13s
Run `debug_line` fuzz target	5m 6s
Run `eh_frame` fuzz target	5m 7s
Run `eh_frame_hdr` fuzz target	5m 10s
	46m 23s

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