Fix typo in comment.

llvm-svn: 231622
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index bc5c155..aaf29db 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -3184,7 +3184,7 @@
     Diag(AtLoc, diag::err_objc_exceptions_disabled) << "@throw";
 
   if (!Throw) {
-    // @throw without an expression designates a rethrow (which much occur
+    // @throw without an expression designates a rethrow (which must occur
     // in the context of an @catch clause).
     Scope *AtCatchParent = CurScope;
     while (AtCatchParent && !AtCatchParent->isAtCatchScope())