cleanup: make Name and STRING_WITH_LEN usable in constexpr

include/m_string.h

@@ -201,7 +201,7 @@ extern ulonglong strtoull(const char *str, char **ptr, int base);
 
 #ifdef __cplusplus
 #include <type_traits>
-template<typename T> inline const char *_swl_check(T s)
+template<typename T> inline constexpr const char *_swl_check(T s)
 {
   static_assert(std::is_same<T, const char (&)[sizeof(T)]>::value
              || std::is_same<T, const char [sizeof(T)]>::value,

sql/sql_type.h

@@ -3384,17 +3384,12 @@ class Type_cast_attributes
 class Name: private LEX_CSTRING
 {
 public:
-  Name(const char *str_arg, uint length_arg)
-  {
-    DBUG_ASSERT(length_arg < UINT_MAX32);
-    LEX_CSTRING::str= str_arg;
-    LEX_CSTRING::length= length_arg;
-  }
-  Name(const LEX_CSTRING &lcs)
-  {
-    LEX_CSTRING::str= lcs.str;
-    LEX_CSTRING::length= lcs.length;
-  }
+  constexpr Name(const char *str_arg, uint length_arg) :
+    LEX_CSTRING({str_arg, length_arg})
+  { }
+  constexpr Name(const LEX_CSTRING &lcs) :
+    LEX_CSTRING(lcs)
+  { }
   const char *ptr() const { return LEX_CSTRING::str; }
   uint length() const { return (uint) LEX_CSTRING::length; }
   const LEX_CSTRING &lex_cstring() const { return *this; }