[clang] [Clang] Allow the use of consecutive brackets as an extension in C++03 (PR #75148)

[via cfe-commits]

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@@ -815,8 +815,8 @@ def err_unexpected_template_in_destructor_name : Error<
   "'template' keyword not permitted in destructor name">;
 def err_unexpected_template_after_using : Error<
   "'template' keyword not permitted after 'using' keyword">;
-def err_two_right_angle_brackets_need_space : Error<
-  "a space is required between consecutive right angle brackets (use '> >')">;
+def err_two_right_angle_brackets_need_space : ExtWarn<
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zmodem wrote:

nit: I think `ext_` is the more common diag prefix for `ExtWarn`

https://github.com/llvm/llvm-project/pull/75148