Cleanup FX macros

This CL renames the FX_OS defines to have _OS_ in their names and drops
the _DESKTOP suffix. The FXM defines have been changed to just FX.

Change-Id: Iab172fba541713b5f6d14fb8098baf68e3364c74
Reviewed-on: https://pdfium-review.googlesource.com/14833
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/javascript/util.cpp b/fpdfsdk/javascript/util.cpp
index 04f1eb3..3fe7a86 100644
--- a/fpdfsdk/javascript/util.cpp
+++ b/fpdfsdk/javascript/util.cpp
@@ -24,7 +24,7 @@
 #include "fpdfsdk/javascript/cjs_runtime.h"
 #include "fpdfsdk/javascript/resource.h"
 
-#if _FX_OS_ == _FX_ANDROID_
+#if _FX_OS_ == _FX_OS_ANDROID_
 #include <ctype.h>
 #endif