Same motivation as #136287, but for a newly introduced test. Rather than
over-constraining here, we just match the sret and accept pretty much
all other attributes.
@rustbot label llvm-main
r? @nikic
Fix codegen of uninhabited PassMode::Indirect return types.
Add codegen test for uninhabited PassMode::Indirect return types.
Enable optimizations for uninhabited return type codegen test