Dont build version if compiling for IOS

Author: igorcanadi

util/build_version.h

@@ -4,10 +4,13 @@
 //  of patent rights can be found in the PATENTS file in the same directory.
 //
 #pragma once
+#if !defined(IOS_CROSS_COMPILE)
+// if we compile with Xcode, we don't run build_detect_vesion, so we don't
+// generate these variables
 // these variables tell us about the git config and time
 extern const char* rocksdb_build_git_sha;
 
 // these variables tell us when the compilation occurred
 extern const char* rocksdb_build_compile_time;
 extern const char* rocksdb_build_compile_date;
-
+#endif