Rebase to upstream #159

Job	Run time
abi-dump-setup	1m 1s
Build lldb / Lit Tests (ubuntu-latest)	3h 22m 13s
Test llvm,clang,libclc / Lit Tests (ubuntu-latest)	4h 35m 53s
Test lld / Lit Tests (ubuntu-latest)	1h 56m 35s
Build lldb / Lit Tests (windows-2019)	2m 18s
Test lld / Lit Tests (windows-2019)	1m 47s
Build lldb / Lit Tests (macOS-latest)	1h 37m 51s
Test llvm,clang,libclc / Lit Tests (windows-2019)	2m 1s
Test lld / Lit Tests (macOS-latest)	1h 3m 39s
Test llvm,clang,libclc / Lit Tests (macOS-latest)	6h 0m 9s
abi-dump (build-baseline)	47m 6s
abi-dump (build-latest)	45m 11s
abi-compare	34s
	20h 16m 18s

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