[clang] Fix crash and improve diagnostics for void lambda returns (PR #188904)

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+// RUN: %clang_cc1 -std=c++20 -fblocks -fsyntax-only -verify %s
+
+void test_lambdas() {
+  (void) [] () -> void { return {}; }; // expected-error {{void lambda should not return a value}}
+  (void) [] () -> void { return {1}; }; // expected-error {{void lambda should not return a value}}
+  (void) [] () -> void { return {1, 2}; }; // expected-error {{void lambda should not return a value}}
+  (void) [] () -> void { return 42; }; // expected-error {{void lambda should not return a value}}
+  (void) [] () -> void { return double(32); }; // expected-error {{void lambda should not return a value}}
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Sirraide wrote:

#192555

https://github.com/llvm/llvm-project/pull/188904