Fixed ANSI C compiler issue

code/M3D/m3d.h

@@ -87,19 +87,15 @@ typedef uint16_t M3D_INDEX;
 #ifndef _MSC_VER
 #define _inline __inline__
 #define _pack __attribute__((packed))
-#  ifdef __cplusplus // only for c++ code
-#    define _unused __attribute__((unused))
-#  else // or c code just use void
-#    define _unused (void)
-#  endif
+#define _unused __attribute__((unused))
 #else
 #define _inline
 #define _pack
-#  ifdef __cplusplus // only for c++ code
+#  ifdef __cplusplus /* only for c++ code */
 #    define _unused __pragma(warning(suppress:4100))
-#  else // or c code just use void
+#  else
 #    define _unused (void)
-#  endif // ___cplusplus
+#  endif
 #endif
 #ifndef  __cplusplus
 #define _register register