reame macro X to TREMOLO_X to fix compiling error, X is not a good name (#228)

sources/tremolo/Tremolo/os_types.h

@@ -18,10 +18,10 @@
 #define _OS_TYPES_H
 
 #ifdef _LOW_ACCURACY_
-#  define X(n) (((((n)>>22)+1)>>1) - ((((n)>>22)+1)>>9))
+#  define TREMOLO_X(n) (((((n)>>22)+1)>>1) - ((((n)>>22)+1)>>9))
 #  define LOOKUP_T const unsigned char
 #else
-#  define X(n) (n)
+#  define TREMOLO_X(n) (n)
 #  define LOOKUP_T const ogg_int32_t
 #endif