add feature dwarf #384

Job	Run time
Cargo fmt	5s
build (macos-11, stable)	6m 59s
Conformance Tests	27m 0s
Dwarf feature	49m 59s
build (macos-11, 1.48.0)	11m 39s
build (windows-2019, stable)	6m 32s
build (windows-2019, 1.48.0)	13m 14s
build (ubuntu-20.04, stable)	8m 37s
build (ubuntu-20.04, 1.48.0)	15m 42s
build (ubuntu-20.04, nightly)	9m 3s
build (ubuntu-20.04, beta)	7m 48s
build (ubuntu-20.04, i686-unknown-linux-gnu, stable)	7m 43s
build (windows-2019, i686-pc-windows-msvc, stable)	7m 24s
build (ubuntu-20.04, clang, clang++, stable)	5m 54s
build (ubuntu-20.04, gcc-7, g++-7, stable)	7m 20s
build (ubuntu-20.04, clang-7, clang++-7, stable)	7m 56s
	3h 12m 55s

Provide feedback