Collapse all uses of target.options.foo into target.foo

with an eye on merging `TargetOptions` into `Target`.

`TargetOptions` as a separate structure is mostly an implementation detail of `Target` construction, all its fields logically belong to `Target` and available from `Target` through `Deref` impls.

compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs

@@ -67,5 +67,5 @@ pub fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool {
 
     !omit_gdb_pretty_printer_section
         && cx.sess().opts.debuginfo != DebugInfo::None
-        && cx.sess().target.options.emit_debug_gdb_scripts
+        && cx.sess().target.emit_debug_gdb_scripts
 }