versioner: introduce.

Add a clang-based tool to inspect header availability attributes and
verify them against the NDK platform definitions.

Bug: http://b/28178111
Change-Id: I1bb1925a620e98cc9606cb5a3360b1224c700bd0
diff --git a/tools/versioner/tests/inline/headers/foo.h b/tools/versioner/tests/inline/headers/foo.h
new file mode 100644
index 0000000..7a48a72
--- /dev/null
+++ b/tools/versioner/tests/inline/headers/foo.h
@@ -0,0 +1,7 @@
+#if __ANDROID_API__ <= 9
+static int foo() __attribute__((availability(android, introduced = 9))) {
+  return 0;
+}
+#else
+int foo() __attribute__((availability(android, introduced = 9)));
+#endif