Index: flang/runtime/file.cpp
===================================================================
--- flang/runtime/file.cpp
+++ flang/runtime/file.cpp
@@ -14,7 +14,7 @@
 #include <cstring>
 #include <fcntl.h>
 #include <stdlib.h>
-#ifdef _WIN32
+#ifdef _MSC_VER
 #define NOMINMAX
 #include <io.h>
 #include <windows.h>
@@ -31,7 +31,7 @@
 }
 
 static int openfile_mkstemp(IoErrorHandler &handler) {
-#ifdef _WIN32
+#ifdef _MSC_VER
   const unsigned int uUnique{0};
   // GetTempFileNameA needs a directory name < MAX_PATH-14 characters in length.
   // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamea