Add a new symlink pointing to the last stable clang version

The purpose of the symlink is to make it easy to reference the latest
stable version of the clang prebuilt in a project built from android
gerrit but outside of the platform build system. The symlink should be
updated to the following version when the prebuilt clang is updated.

Change-Id: Iea94739f65fad4d5cda9e6257bc902dcec854e8a
diff --git a/clang-stable b/clang-stable
new file mode 120000
index 0000000..a57f773
--- /dev/null
+++ b/clang-stable
@@ -0,0 +1 @@
+clang-2812033/
\ No newline at end of file