Address review feedback

  - Add [[maybe_unused]] to suppress unused variable warning
  - Add C++98 test case
  - Fix missing newline

Author: Jongmyeong Choi

clang/lib/Sema/SemaOverload.cpp

@@ -6275,8 +6275,8 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
                                                    QualType T, CCEKind CCE,
                                                    NamedDecl *Dest,
                                                    APValue &PreNarrowingValue) {
-  bool isCCEAllowedPreCXX11 =
-    (CCE == CCEKind::TempArgStrict || CCE == CCEKind::ExplicitBool);
+  [[maybe_unused]] bool isCCEAllowedPreCXX11 =
+      (CCE == CCEKind::TempArgStrict || CCE == CCEKind::ExplicitBool);
   assert((S.getLangOpts().CPlusPlus11 || isCCEAllowedPreCXX11) &&
          "converted constant expression outside C++11 or TTP matching");
 

clang/test/Parser/explicit-bool-pre-cxx17.cpp

@@ -1,5 +1,6 @@
 // Regression test for assertion failure when explicit(bool) is used in pre-C++20
 // Fixes GitHub issue #152729
+// RUN: %clang_cc1 -std=c++98 -verify %s
 // RUN: %clang_cc1 -std=c++03 -verify %s
 // RUN: %clang_cc1 -std=c++11 -verify %s
 // RUN: %clang_cc1 -std=c++14 -verify %s
@@ -11,4 +12,4 @@ struct S {
 
   explicit(false) S(float);
   // expected-warning@-1 {{explicit(bool) is a C++20 extension}}
-};
+};