clarify iio.h macros that break with MATLAB on Linux

So there's less chance of them getting inadvertantly synced over again.

iio.h

@@ -37,9 +37,16 @@ extern "C" {
 typedef long ssize_t;
 #endif
 
+/* Breaks with MATLAB on Linux
+ * #ifdef __GNUC__
+ * #define __cnst __attribute__((const))
+ * #define __pure __attribute__((pure))
+ * #define __notused __attribute__((unused))
+ * #else */
 #define __cnst
 #define __pure
 #define __notused
+/* #endif */
 
 #ifdef _WIN32
 #   ifdef LIBIIO_EXPORTS
@@ -47,6 +54,9 @@ typedef long ssize_t;
 #   else
 #	define __api __declspec(dllimport)
 #   endif
+/* Breaks with MATLAB on Linux
+ * #elif __GNUC__ >= 4
+ * #   define __api __attribute__((visibility ("default"))) */
 #else
 #   define __api
 #endif