versioner: don't always hide future decls.

Bug: http://b/32748732
Test: python run_tests.py
Change-Id: I8f799015ebb1017f5e7d1324fb4c724e12a268bc
diff --git a/tools/versioner/src/Preprocessor.cpp b/tools/versioner/src/Preprocessor.cpp
index da5d250..a52ce53 100644
--- a/tools/versioner/src/Preprocessor.cpp
+++ b/tools/versioner/src/Preprocessor.cpp
@@ -221,7 +221,7 @@
     bool future = avail.arch_availability[*it.second.begin()].future;
 
     if (future) {
-      return "0";
+      return "__ANDROID_API__ >= __ANDROID_API_FUTURE__";
     }
 
     // The maximum min_version of the set.