Get rid of '_WIN32' is not defined warnings

Summary: s/#if _WIN32/#ifdef _WIN32/

Reviewed By: Orvid

Differential Revision: D17738798

fbshipit-source-id: cbfcf67c55b56a5e5453430d127acc3a7116814c

folly/IPAddressV6.cpp

@@ -25,7 +25,7 @@
 #include <folly/MacAddress.h>
 #include <folly/detail/IPAddressSource.h>
 
-#if !_WIN32
+#ifndef _WIN32
 #include <net/if.h>
 #else
 // Because of the massive pain that is libnl, this can't go into the socket

folly/portability/PThread.cpp

@@ -16,7 +16,7 @@
 
 #include <folly/portability/PThread.h>
 
-#if !FOLLY_HAVE_PTHREAD && _WIN32
+#if !FOLLY_HAVE_PTHREAD && defined(_WIN32)
 #include <boost/thread/tss.hpp> // @manual
 
 #include <errno.h>

folly/synchronization/SanitizeThread.cpp

@@ -54,7 +54,7 @@ extern "C" FOLLY_ATTR_WEAK void AnnotateIgnoreSyncBegin(const char* f, int l);
 
 extern "C" FOLLY_ATTR_WEAK void AnnotateIgnoreSyncEnd(const char* f, int l);
 
-#if _MSC_VER
+#ifdef _MSC_VER
 #define FOLLY_SANITIZE_THREAD_CALL_HOOK(name, ...) [](...) {}(__VA_ARGS__)
 #else
 #define FOLLY_SANITIZE_THREAD_CALL_HOOK(name, ...) name(__VA_ARGS__)