Fixed some buggy edge-cases in UseOverrideCheck.cpp

[baxtersa]

Summary

Fix modernize-use-override bug when overriding const function ending with '...const= 0' by inserting additional space in replacement text
Added case to catch virtual throwing functions with no function body in header

[baxtersa]

I don't know who to add as reviewers here, so if someone in the know could do that that would be great!

clang-tidy/modernize/UseOverrideCheck.cpp

if (!HasFinal && !HasOverride) {
     if (!InsertLoc.isValid()) {
       // For declarations marked with "= 0" or "= [default|delete]", the end
       // location will point until after those markings. Therefore, the override
       // keyword shouldn't be inserted at the end, but before the '='.
       if (Tokens.size() > 2 && (GetText(Tokens.back(), Sources) == "0" ||
                                 Tokens.back().is(tok::kw_default) ||
                                 Tokens.back().is(tok::kw_delete)) &&
           GetText(Tokens[Tokens.size() - 2], Sources) == "=") {
+          
+        if (Tokens.size() > 3 &&
+            GetText(Tokens[Tokens.size() - 3], Sources) == "const" &&
+            Tokens[Tokens.size() - 2].getLocation() ==
+              Tokens[Tokens.size() - 3].getEndLoc()) {
+            ReplacementText = " override";
+        }
+          
         InsertLoc = Tokens[Tokens.size() - 2].getLocation();
       } else if (GetText(Tokens.back(), Sources) == "ABSTRACT") {
         InsertLoc = Tokens.back().getLocation();
       }
     }
       
     if (!InsertLoc.isValid()) {
+      // For declarations marked with "throw(...)", the override keyword
+      // should be inserted last, immediately before the ending semi-colon
+      Token ThrowToken;
+      for (Token T : Tokens) {
+        if (T.is(tok::kw_throw)) {
+            ThrowToken = T;
+            break;
+        }
+      }
+      if (ThrowToken.is(tok::kw_throw)) {
+        Token LastNonCommentToken;
+        for (Token T : Tokens) {
+            if (!T.is(tok::comment)) {
+                LastNonCommentToken = T;
+            }
+        }
+        InsertLoc = LastNonCommentToken.getEndLoc();
+        ReplacementText = " override";
+      }
+    }
+
+    if (!InsertLoc.isValid()) {
       InsertLoc = FileRange.getEnd();
       ReplacementText = " override";
     }
     Diag << FixItHint::CreateInsertion(InsertLoc, ReplacementText);
   }
 
   if (HasFinal && HasOverride) {
     SourceLocation OverrideLoc = Method->getAttr<OverrideAttr>()->getLocation();