suggest fix for attempted integer identifier in patterns

compiler/rustc_mir_build/src/errors.rs

@@ -770,6 +770,8 @@ pub(crate) struct PatternNotCovered<'s, 'tcx> {
     #[subdiagnostic]
     pub let_suggestion: Option<SuggestLet>,
     #[subdiagnostic]
+    pub misc_suggestion: Option<MiscPatternSuggestion>,
+    #[subdiagnostic]
     pub res_defined_here: Option<ResDefinedHere>,
 }
 
@@ -848,3 +850,16 @@ pub enum SuggestLet {
         count: usize,
     },
 }
+
+#[derive(Subdiagnostic)]
+pub enum MiscPatternSuggestion {
+    #[suggestion(
+        mir_build_suggest_attempted_int_lit,
+        code = "_",
+        applicability = "maybe-incorrect"
+    )]
+    AttemptedIntegerLiteral {
+        #[primary_span]
+        start_span: Span,
+    },
+}