Fix checking whether _WIN32 is defined

Bug 29329
diff --git a/poppler/StdinCachedFile.cc b/poppler/StdinCachedFile.cc
index 5747572..3a91e62 100644
--- a/poppler/StdinCachedFile.cc
+++ b/poppler/StdinCachedFile.cc
@@ -25,7 +25,7 @@
   size_t read, size = 0;
   char buf[CachedFileChunkSize];
 
-#if _WIN32
+#ifdef _WIN32
   setmode(fileno(stdin), O_BINARY);
 #endif
 
diff --git a/utils/pdftoppm.cc b/utils/pdftoppm.cc
index 14950d0..c4cc43b 100644
--- a/utils/pdftoppm.cc
+++ b/utils/pdftoppm.cc
@@ -183,7 +183,7 @@
       bitmap->writePNMFile(ppmFile);
     }
   } else {
-#if _WIN32
+#ifdef _WIN32
     setmode(fileno(stdout), O_BINARY);
 #endif