Cleanup CodegenFnAttrFlags

- Rename `USED` to `USED_COMPILER` to better reflect its behavior.
- Reorder some items to group the used and allocator flags together
- Renumber them without gaps

Author: Noratrieb

src/bin/miri.rs

@@ -281,7 +281,7 @@ impl rustc_driver::Callbacks for MiriBeRustCompilerCalls {
                             }
                             let codegen_fn_attrs = tcx.codegen_fn_attrs(local_def_id);
                             if codegen_fn_attrs.contains_extern_indicator()
-                                || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::USED)
+                                || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER)
                                 || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
                             {
                                 Some((

src/helpers.rs

@@ -135,7 +135,7 @@ pub fn iter_exported_symbols<'tcx>(
             let codegen_attrs = tcx.codegen_fn_attrs(def_id);
             codegen_attrs.contains_extern_indicator()
                 || codegen_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
-                || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED)
+                || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER)
                 || codegen_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
         };
         if exported {