Rollup merge of #120502 - clubby789:remove-ffi-returns-twice, r=compiler-errors

Remove `ffi_returns_twice` feature

The [tracking issue](https://github.com/rust-lang/rust/issues/58314) and [RFC](https://github.com/rust-lang/rfcs/pull/2633) have been closed for a couple of years.

There is also an attribute gate in R-A which should be removed if this lands.

compiler/rustc_llvm/llvm-wrapper/LLVMWrapper.h

@@ -76,7 +76,6 @@ enum LLVMRustAttribute {
   SanitizeMemory = 22,
   NonLazyBind = 23,
   OptimizeNone = 24,
-  ReturnsTwice = 25,
   ReadNone = 26,
   SanitizeHWAddress = 28,
   WillReturn = 29,

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -250,8 +250,6 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
     return Attribute::NonLazyBind;
   case OptimizeNone:
     return Attribute::OptimizeNone;
-  case ReturnsTwice:
-    return Attribute::ReturnsTwice;
   case ReadNone:
     return Attribute::ReadNone;
   case SanitizeHWAddress: