MDEV-26443 HAVE_C99_INITIALIZERS is not applicable to C++

Designated initializers were introduced in ISO/IEC 9899:1999 (C99),
but the C code base of MariaDB is supposed to be compatible with the
1990 version of the standard.

The InnoDB code based was switched from C to C++ in
MySQL 5.6 and MariaDB 10.0. C++ did not introduce syntax for
designated initializers until ISO/IEC 14882:2020.
Our C++ code base is still stuck with the 2011 or earlier version of
that standard.

Therefore, this check as well as the macro STRUCT_FLD are best removed.

storage/innobase/handler/i_s.h

@@ -92,26 +92,9 @@ do {									\
 	}								\
 } while (0)
 
-#if !defined __STRICT_ANSI__ && defined __GNUC__ && (__GNUC__) > 2 && !defined __INTEL_COMPILER && !defined __clang__
-#ifdef HAVE_C99_INITIALIZERS
-#define STRUCT_FLD(name, value)	.name = value
-#else
-#define STRUCT_FLD(name, value)	name: value
-#endif /* HAVE_C99_INITIALIZERS */
-#else
-#define STRUCT_FLD(name, value)	value
-#endif
-
 /* Don't use a static const variable here, as some C++ compilers (notably
 HPUX aCC: HP ANSI C++ B3910B A.03.65) can't handle it. */
-#define END_OF_ST_FIELD_INFO \
-	{STRUCT_FLD(field_name,		NULL), \
-	 STRUCT_FLD(field_length,	0), \
-	 STRUCT_FLD(field_type,		MYSQL_TYPE_NULL), \
-	 STRUCT_FLD(value,		0), \
-	 STRUCT_FLD(field_flags,	0), \
-	 STRUCT_FLD(old_name,		""), \
-	 STRUCT_FLD(open_method,	SKIP_OPEN_TABLE)}
+#define END_OF_ST_FIELD_INFO {NULL,0,MYSQL_TYPE_NULL,0,0,"",SKIP_OPEN_TABLE}
 
 /** Fields on INFORMATION_SCHEMA.SYS_SEMAMPHORE_WAITS table */
 #define SYS_SEMAPHORE_WAITS_THREAD_ID	0

storage/innobase/innodb.cmake

@@ -228,11 +228,6 @@ ENDIF(NOT MSVC)
 
 CHECK_FUNCTION_EXISTS(vasprintf  HAVE_VASPRINTF)
 
-CHECK_CXX_SOURCE_COMPILES("struct t1{ int a; char *b; }; struct t1 c= { .a=1, .b=0 }; main() { }" HAVE_C99_INITIALIZERS)
-IF(HAVE_C99_INITIALIZERS)
-  ADD_DEFINITIONS(-DHAVE_C99_INITIALIZERS)
-ENDIF()
-
 SET(MUTEXTYPE "event" CACHE STRING "Mutex type: event, sys or futex")
 
 IF(MUTEXTYPE MATCHES "event")