[clang] Fix crash with invalid member function param list (PR #139595)

[Erich Keane via cfe-commits]

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@@ -40,3 +40,13 @@ struct S : public Base1<int>, public Base2<float> {
   // All initializers are correct, nothing to skip, diagnose 2 missing commas.
   S(const S &) : Base1<int>(0) ::Base2<float>(1.0) x(2) {} // expected-error2{{missing ',' between base or member initializers}}
 };
+
+namespace GH113722 {
+struct S {
+  void m(int x = 0;   // expected-error {{unexpected end of default argument expression}} \
+                         expected-note {{to match this '('}}
+    #pragma unused(x) // expected-error {{expected ')'}} \
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erichkeane wrote:

OH! missed that this was a function parameter/default argument and part of one that is already ill-formed.  I thinks this recovery makes sense, I don't see any need for other tests

https://github.com/llvm/llvm-project/pull/139595