add feature dwarf #381

Job	Run time
Conformance Tests	31m 35s
Dwarf feature	45m 13s
Cargo fmt	12s
build (macos-11, stable)	7m 3s
build (macos-11, 1.48.0)	11m 39s
build (windows-2019, stable)	7m 53s
build (windows-2019, 1.48.0)	11m 20s
build (ubuntu-20.04, stable)	10m 37s
build (ubuntu-20.04, 1.48.0)	16m 1s
build (ubuntu-20.04, nightly)	7m 24s
build (ubuntu-20.04, beta)	9m 27s
build (ubuntu-20.04, i686-unknown-linux-gnu, stable)	10m 35s
build (windows-2019, i686-pc-windows-msvc, stable)	6m 16s
build (ubuntu-20.04, clang, clang++, stable)	5m 49s
build (ubuntu-20.04, gcc-7, g++-7, stable)	8m 13s
build (ubuntu-20.04, clang-7, clang++-7, stable)	8m 3s
build (ubuntu-18.04, stable)	1s
build (ubuntu-18.04, 1.48.0)	1s
	3h 17m 22s

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