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

Remove `ffi_returns_twice` feature

The [tracking issue](rust-lang#58314) and [RFC](rust-lang/rfcs#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.

Author: matthiaskrgr

src/attributes.rs

@@ -62,9 +62,6 @@ pub fn from_fn_attrs<'gcc, 'tcx>(
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
             func.add_attribute(FnAttribute::Cold);
         }
-        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_RETURNS_TWICE) {
-            func.add_attribute(FnAttribute::ReturnsTwice);
-        }
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_PURE) {
             func.add_attribute(FnAttribute::Pure);
         }