Test for _WIN32 in frameworks/rs instead of USE_MINGW.

Bug: http://b/23392815
Test: builds
Change-Id: I9c61f4223abe5a37bbce2bc99a742aaf4199f30f
diff --git a/rsScriptC.cpp b/rsScriptC.cpp
index b4d364f..6508e7f 100644
--- a/rsScriptC.cpp
+++ b/rsScriptC.cpp
@@ -32,12 +32,12 @@
 #include <sstream>
 #include <string>
 
-#ifdef USE_MINGW
+#ifdef _WIN32
 /* Define the default path separator for the platform. */
 #define OS_PATH_SEPARATOR     '\\'
 #define OS_PATH_SEPARATOR_STR "\\"
 
-#else /* not USE_MINGW */
+#else /* not _WIN32 */
 
 /* Define the default path separator for the platform. */
 #define OS_PATH_SEPARATOR     '/'