[WIP] Remove dependency on enable_multi_ret_implicit_sret #1044

Job	Run time
abi_cafe (macos-latest, aarch64-apple-darwin)	3m 14s
abi_cafe (macos-latest, x86_64-apple-darwin)	12m 44s
abi_cafe (ubuntu-latest, x86_64-unknown-linux-gnu)	3m 22s
abi_cafe (windows-latest, x86_64-pc-windows-msvc)	12m 32s
	31m 52s

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