[Clang] [AST] Resolve FIXME: Assign E to nullptr (#84229)

We do not support GCC 4.8 anymore.

Author: AZero13

clang/include/clang/AST/Expr.h

@@ -5843,7 +5843,7 @@ class GenericSelectionExpr final
         std::conditional_t<Const, const Stmt *const *, Stmt **>;
     using TSIPtrPtrTy = std::conditional_t<Const, const TypeSourceInfo *const *,
                                            TypeSourceInfo **>;
-    StmtPtrPtrTy E; // = nullptr; FIXME: Once support for gcc 4.8 is dropped.
+    StmtPtrPtrTy E = nullptr;
     TSIPtrPtrTy TSI; // Kept in sync with E.
     unsigned Offset = 0, SelectedOffset = 0;
     AssociationIteratorTy(StmtPtrPtrTy E, TSIPtrPtrTy TSI, unsigned Offset,