Fix __attribute__(A) macro (it formerly used bogus __cplusplus__ symbol)

include/my_global.h:
  Change __cplusplus__ to __cplusplus in #define __attribute__(A) macro

include/my_global.h

@@ -473,7 +473,7 @@ typedef unsigned short ushort;
 #  define __attribute__(A)
 # elif GCC_VERSION < 2008
 #  define __attribute__(A)
-# elif defined(__cplusplus__) && GCC_VERSION < 3004
+# elif defined(__cplusplus) && GCC_VERSION < 3004
 #  define __attribute__(A)
 # endif
 #endif