THRIFT-3437 Fixed MinGW-w64 build

A small follow-up fix:
Avoid redefinition of AI_ADDRCONFIG on non-Windows platforms.
diff --git a/lib/cpp/src/thrift/server/TNonblockingServer.cpp b/lib/cpp/src/thrift/server/TNonblockingServer.cpp
index 96ee517..1e35275 100644
--- a/lib/cpp/src/thrift/server/TNonblockingServer.cpp
+++ b/lib/cpp/src/thrift/server/TNonblockingServer.cpp
@@ -69,7 +69,7 @@
 #define PRIu64 "I64u"
 #endif
 
-#if (_WIN32_WINNT < 0x0600)
+#if defined(_WIN32) && (_WIN32_WINNT < 0x0600)
   #define AI_ADDRCONFIG 0x0400
 #endif