Update C++ checks approach

Signed-off-by: acuadros95 <acuadros1995@gmail.com>

include/rosidl_dynamic_typesupport/uchar.h

@@ -19,14 +19,15 @@
 extern "C" {
 #endif
 
-
-#if defined __has_include
-#  if __has_include(<uchar.h>)
-#    include <uchar.h>
-#    define INCLUDED_UCHAR 1
-#  endif
-#endif
-#if !defined(INCLUDED_UCHAR) && __cplusplus <= 199711L
+#if defined(__cplusplus) && __cplusplus >= 201103L
+// Nothing to do here, C++11 and beyond have char16_t as a keyword:
+// https://en.cppreference.com/w/cpp/keyword/char16_t
+#elif defined(__has_include) && __has_include(<uchar.h>)
+// If the compiler has __has_include, and uchar.h exists, include that as it will have char16_t
+// as a typedef.
+#  include <uchar.h>
+#else
+// Otherwise assume that char16_t isn't defined anywhere, and define it ourselves as uint_least16_t.
 #  include <stdint.h>
 typedef uint_least16_t char16_t;
 #endif