Move some calls to before calling codegen_crate

`--emit mir`, `#[rustc_symbol_name]` and `#[rustc_def_path]` now run
before codegen and thus work even if codegen fails. This can help with
debugging.

compiler/rustc_driver_impl/src/session_diagnostics.rs

@@ -2,6 +2,12 @@ use std::error::Error;
 
 use rustc_macros::{Diagnostic, Subdiagnostic};
 
+#[derive(Diagnostic)]
+#[diag(driver_impl_cant_emit_mir)]
+pub struct CantEmitMIR {
+    pub error: std::io::Error,
+}
+
 #[derive(Diagnostic)]
 #[diag(driver_impl_rlink_unable_to_read)]
 pub(crate) struct RlinkUnableToRead {