[builds/windows] Simplify non-desktop UWP check.

Fixes mingw compilation described in !159.

* builds/windows/ftsystem.c: Do not use WINAPI_FAMILY_PARTITION macro.
diff --git a/builds/windows/ftsystem.c b/builds/windows/ftsystem.c
index 4f4ac15..6557cea 100644
--- a/builds/windows/ftsystem.c
+++ b/builds/windows/ftsystem.c
@@ -197,8 +197,7 @@
 
 
   /* non-desktop Universal Windows Platform */
-#if defined( WINAPI_FAMILY_PARTITION )                 && \
-    !WINAPI_FAMILY_PARTITION( WINAPI_PARTITION_DESKTOP )
+#if defined( WINAPI_FAMILY ) && WINAPI_FAMILY != WINAPI_FAMILY_DESKTOP_APP
 
 #define PACK_DWORD64( hi, lo )  ( ( (DWORD64)(hi) << 32 ) | (DWORD)(lo) )