Split LLVM intrinsic abi handling from the rest of the abi handling

[bjorn3]

LLVM intrinsics have weird requirements like requiring the fake "unadjusted" abi, not being callable through function pointers and for all codegen backends other than cg_llvm requiring special cases to redirect them to the correct backend specific intrinsic (or directly codegen their implementation inline without any intrinsic call). By splitting the LLVM intrinsic handling it becomes easier for backends to special case them and should in the future allow getting rid of the abi calculation for extern "unadjusted" in favor of computing the correct abi directly in the backend without depending on the exact way cg_ssa lowers types.

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[rustbot]

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[bjorn3]

cc @sayantn This should make #140763 much less intrusive for the non-intrinsic call handling and should allow you to localize all changes to cg_llvm without having to touch cg_ssa and cg_gcc.

[sayantn]

this is awesome, thanks ❤️. I tested compiling stdarch with this branch (for x86_64-unknown-linux-gnu, aarch64-unknown-linux-gnu and riscv64gc-unknown-linux-gnu targets), it doesn't generate any errors

[bjorn3]

Thanks for testing! I hadn't thought about testing this on stdarch. Did you also test compiling the stdarch tests? Otherwise no llvm intrinsic calls are actually getting codegened I think due to all #[inline(always)].

[sayantn]

yes, I did cargo build -p core_arch --tests, which will compile all intrinsics in x86 (due to all intrinsics having corresponding tests), I am not so sure about aarch64, there can be some intrinsics that are not tested.