[flang] One more fix for dumping evaluate::Expr (llvm#165730)

Clang doesn't have "std::string_view" in the type list.

Author: kparzysz

flang/include/flang/Semantics/dump-expr.h

@@ -48,10 +48,11 @@ class DumpEvaluateExpr {
       // "... [with T = xyz; std::string_view = ...]"
 #ifdef __clang__
       std::string_view front("[T = ");
+      std::string_view back("]");
 #else
       std::string_view front("[with T = ");
-#endif
       std::string_view back("; std::string_view =");
+#endif
 
 #elif defined(_MSC_VER)
 #define DUMP_EXPR_SHOW_TYPE