zlibWrapper: Update for zlib 1.2.12 (#3217)

In zlib 1.2.12 the OF macro was changed to _Z_OF breaking any
project that used zlibWrapper. To fix this the OF has been
changed to _Z_OF everywhere and _Z_OF is defined as OF in the
case it is not yet defined for zlib 1.2.11 and older.

Fixes: https://github.com/facebook/zstd/issues/3216

zlibWrapper/zstd_zlibwrapper.h

@@ -25,6 +25,9 @@ extern "C" {
     #define z_const
 #endif
 
+#if !defined(_Z_OF)
+    #define _Z_OF OF
+#endif
 
 /* returns a string with version of zstd library */
 const char * zstdVersion(void);