Improve check for Windows platforms

Instead of checking for compiler, check for platform.
diff --git a/src/hb-atomic-private.hh b/src/hb-atomic-private.hh
index c7456e0..bb10fe1 100644
--- a/src/hb-atomic-private.hh
+++ b/src/hb-atomic-private.hh
@@ -42,7 +42,7 @@
 #if 0
 
 
-#elif !defined(HB_NO_MT) && (defined(_MSC_VER) || defined(__MINGW32__))
+#elif !defined(HB_NO_MT) && (defined(_WIN32) || defined(__CYGWIN__))
 
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
diff --git a/src/hb-mutex-private.hh b/src/hb-mutex-private.hh
index fcbdb31..0fb21c2 100644
--- a/src/hb-mutex-private.hh
+++ b/src/hb-mutex-private.hh
@@ -42,7 +42,7 @@
 #if 0
 
 
-#elif !defined(HB_NO_MT) && (defined(_MSC_VER) || defined(__MINGW32__))
+#elif !defined(HB_NO_MT) && (defined(_WIN32) || defined(__CYGWIN__))
 
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>