compiler: Directly use rustc_abi in metadata and middle

Stop reexporting ReprOptions from middle::ty

compiler/rustc_middle/src/mir/syntax.rs

@@ -3,6 +3,7 @@
 //! This is in a dedicated file so that changes to this file can be reviewed more carefully.
 //! The intention is that this file only contains datatype declarations, no code.
 
+use rustc_abi::{FieldIdx, VariantIdx};
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece, Mutability};
 use rustc_data_structures::packed::Pu128;
 use rustc_hir::CoroutineKind;
@@ -13,7 +14,6 @@ use rustc_span::Span;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::Symbol;
-use rustc_target::abi::{FieldIdx, VariantIdx};
 use rustc_target::asm::InlineAsmRegOrRegClass;
 use smallvec::SmallVec;