rapidjson.h: add forgotten ppc64 case
diff --git a/include/rapidjson/rapidjson.h b/include/rapidjson/rapidjson.h
index 5ea6947..247b8e6 100644
--- a/include/rapidjson/rapidjson.h
+++ b/include/rapidjson/rapidjson.h
@@ -268,7 +268,7 @@
 #  elif defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
 #    define RAPIDJSON_ENDIAN RAPIDJSON_BIGENDIAN
 // Detect with architecture macros
-#  elif defined(__sparc) || defined(__sparc__) || defined(_POWER) || defined(__powerpc__) || defined(__ppc__) || defined(__hpux) || defined(__hppa) || defined(_MIPSEB) || defined(_POWER) || defined(__s390__)
+#  elif defined(__sparc) || defined(__sparc__) || defined(_POWER) || defined(__powerpc__) || defined(__ppc__) || defined(__ppc64__) || defined(__hpux) || defined(__hppa) || defined(_MIPSEB) || defined(_POWER) || defined(__s390__)
 #    define RAPIDJSON_ENDIAN RAPIDJSON_BIGENDIAN
 #  elif defined(__i386__) || defined(__alpha__) || defined(__ia64) || defined(__ia64__) || defined(_M_IX86) || defined(_M_IA64) || defined(_M_ALPHA) || defined(__amd64) || defined(__amd64__) || defined(_M_AMD64) || defined(__x86_64) || defined(__x86_64__) || defined(_M_X64) || defined(__bfin__)
 #    define RAPIDJSON_ENDIAN RAPIDJSON_LITTLEENDIAN