No longer issue static lambda pedantic warning for pre-c++2b compat

We were accidentally issuing "static lambdas are incompatible with C++
standards before C++2b" with -pedantic because it was an ExtWarn
diagnostic rather than a Warning. This corrects the diagnostic category
and adds some test coverage.

Fixes #61582

(cherry picked from commit b904e68)

clang/docs/ReleaseNotes.rst

@@ -779,8 +779,8 @@ Bug Fixes to Attribute Support
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
 - No longer issue a pre-C++2b compatibility warning in ``-pedantic`` mode
-  regading overloaded `operator[]` with more than one parmeter. (`#61582
-  <https://github.com/llvm/llvm-project/issues/61582>`_)
+  regading overloaded `operator[]` with more than one parmeter or for static
+  lambdas. (`#61582 <https://github.com/llvm/llvm-project/issues/61582>`_)
 
 - Address the thread identification problems in coroutines.
   (`#47177 <https://github.com/llvm/llvm-project/issues/47177>`_,

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1052,7 +1052,7 @@ def err_lambda_template_parameter_list_empty : Error<
 // C++2b static lambdas
 def err_static_lambda: ExtWarn<
   "static lambdas are a C++2b extension">, InGroup<CXX2b>;
-def warn_cxx20_compat_static_lambda: ExtWarn<
+def warn_cxx20_compat_static_lambda : Warning<
   "static lambdas are incompatible with C++ standards before C++2b">,
   InGroup<CXXPre2bCompat>, DefaultIgnore;
 def err_static_mutable_lambda : Error<

clang/test/Parser/cxx2b-lambdas-ext-warns.cpp

@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -std=c++20 %s -verify=cxx20
 // RUN: %clang_cc1 -std=c++2b %s -verify=cxx2b
 // RUN: %clang_cc1 -std=c++2b -Wpre-c++2b-compat %s -verify=precxx2b
+// RUN: %clang_cc1 -std=c++2b -pedantic %s -verify=cxx2b
 
 //cxx2b-no-diagnostics